Anything in the Jenkins log that indicates a failure to load the Matrix Project plugin?

Not that I can see. And the matrix project run fins without problems if they are triggered manually. Here's the full log from restart to the first error:

jun 10, 2015 3:29:00 EM hudson.util.RobustReflectionConverter doUnmarshal
WARNING: Cannot convert type hudson.plugins.git.Revision to type org.eclipse.jgit.lib.ObjectId
jun 10, 2015 3:29:21 EM jenkins.model.Jenkins$23 run
INFO: Restart in 10 seconds
jun 10, 2015 3:29:31 EM jenkins.model.Jenkins$23 run
SEVERE: Restarting VM as requested by magjac
Running from: /usr/share/jenkins/jenkins.war
jun 10, 2015 3:29:33 EM winstone.Logger logInternal
INFO: Beginning extraction from war file
jun 10, 2015 3:29:33 EM org.eclipse.jetty.util.log.JavaUtilLog info
INFO: jetty-winstone-2.8
jun 10, 2015 3:29:35 EM org.eclipse.jetty.util.log.JavaUtilLog info
INFO: NO JSP Support for /jenkins, did not find org.apache.jasper.servlet.JspServlet
Jenkins home directory: /srv/jenkins found at: EnvVars.masterEnvVars.get("JENKINS_HOME")
jun 10, 2015 3:29:35 EM org.eclipse.jetty.util.log.JavaUtilLog info
INFO: Started SelectChannelConnector@0.0.0.0:8080
jun 10, 2015 3:29:35 EM winstone.Logger logInternal
INFO: Winstone Servlet Engine v2.0 running: controlPort=disabled
jun 10, 2015 3:29:36 EM jenkins.InitReactorRunner$1 onAttained
INFO: Started initialization
jun 10, 2015 3:29:37 EM jenkins.InitReactorRunner$1 onAttained
INFO: Listed all plugins
jun 10, 2015 3:29:37 EM hudson.plugins.greenballs.PluginImpl start
INFO: Green Balls!
jun 10, 2015 3:29:37 EM jenkins.InitReactorRunner$1 onAttained
INFO: Prepared all plugins
jun 10, 2015 3:29:37 EM jenkins.InitReactorRunner$1 onAttained
INFO: Started all plugins
jun 10, 2015 3:29:37 EM jenkins.InitReactorRunner$1 onAttained
INFO: Augmented all extensions
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect TEST
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect TEST-TEST
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect TemplateRig
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect common_bist
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect eth_10g
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect eth_ism
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect eth_n3xx
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect eth_n6xx
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect iptrunk_1G_ism_ark
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect iptrunk_TT
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect iptrunk_compression
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect iptrunk_n390_two_nodes
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect iptrunk_sdh_10g
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect iptrunk_switching_n390
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect mutzi
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect netsim2_system_regr
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect netsim_random_50_nodes
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect netsim_system_regr
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect obelix
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect smoke
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect svanen_system_n360_regr
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect svanen_system_n390_regr
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect system_regr
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect va220
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect va220_vpn
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_J2K_1st
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_J2K_2nd
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_access_ARK_MADI
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_access_ARK_VAM_and_ISM
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_access_ISM_DS3E3
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_access_ISM_SDI
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_access_ISM_STM1
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_access_vam
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_access_vam_and_J2K_1st
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_sdi4k
jun 10, 2015 3:29:38 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect {{ JENKINS_SLAVE }}
[06/10/15 15:29:42] SSH Launch of videoaudio_sdi4k on igge.lab.netinsight.se failed in 197 ms
[06/10/15 15:29:42] SSH Launch of va220 on igge.lab.netinsight.se failed in 198 ms
[06/10/15 15:29:42] SSH Launch of iptrunk_switching_n390 on igge.lab.netinsight.se failed in 198 ms
[06/10/15 15:29:42] SSH Launch of videoaudio_J2K_1st on igge.lab.netinsight.se failed in 198 ms
[06/10/15 15:29:42] SSH Launch of TEST on igge.lab.netinsight.se failed in 198 ms
[06/10/15 15:29:42] SSH Launch of svanen_system_n360_regr on igge.lab.netinsight.se failed in 199 ms
[06/10/15 15:29:42] SSH Launch of common_bist on igge.lab.netinsight.se failed in 202 ms
[06/10/15 15:29:42] SSH Launch of videoaudio_access_ISM_SDI on igge.lab.netinsight.se failed in 203 ms
[06/10/15 15:29:42] SSH Launch of eth_ism on igge.lab.netinsight.se failed in 205 ms
[06/10/15 15:29:42] SSH Launch of iptrunk_compression on igge.lab.netinsight.se failed in 205 ms
[06/10/15 15:29:42] SSH Launch of videoaudio_access_ISM_STM1 on igge.lab.netinsight.se failed in 205 ms
[06/10/15 15:29:42] SSH Launch of videoaudio_J2K_2nd on igge.lab.netinsight.se failed in 206 ms
[06/10/15 15:29:42] SSH Launch of iptrunk_TT on igge.lab.netinsight.se failed in 207 ms
[06/10/15 15:29:42] SSH Launch of videoaudio_access_ISM_DS3E3 on igge.lab.netinsight.se failed in 208 ms
[06/10/15 15:29:42] SSH Launch of {{ JENKINS_SLAVE }} on dummy failed in 208 ms
[06/10/15 15:29:42] SSH Launch of iptrunk_sdh_10g on igge.lab.netinsight.se failed in 208 ms
[06/10/15 15:29:42] SSH Launch of netsim_random_50_nodes on igge.lab.netinsight.se failed in 207 ms
[06/10/15 15:29:42] SSH Launch of eth_n6xx on igge.lab.netinsight.se failed in 205 ms
[06/10/15 15:29:42] SSH Launch of iptrunk_n390_two_nodes on igge.lab.netinsight.se failed in 208 ms
[06/10/15 15:29:42] SSH Launch of videoaudio_access_vam_and_J2K_1st on igge.lab.netinsight.se failed in 208 ms
[06/10/15 15:29:42] SSH Launch of videoaudio_access_ARK_MADI on igge.lab.netinsight.se failed in 209 ms
[06/10/15 15:29:42] SSH Launch of svanen_system_n390_regr on igge.lab.netinsight.se failed in 209 ms
[06/10/15 15:29:42] SSH Launch of iptrunk_1G_ism_ark on igge.lab.netinsight.se failed in 215 ms
[06/10/15 15:29:43] SSH Launch of eth_n3xx on igge.lab.netinsight.se failed in 1 652 ms
[06/10/15 15:29:46] SSH Launch of obelix on obelix.netinsight.se completed in 4 162 ms
[06/10/15 15:29:46] SSH Launch of smoke on smoke.netinsight.se completed in 4 719 ms
[06/10/15 15:29:47] SSH Launch of TEST-TEST on igge.lab.netinsight.se completed in 5 883 ms
[06/10/15 15:29:47] SSH Launch of TemplateRig on igge.lab.netinsight.se completed in 5 940 ms
[06/10/15 15:29:47] SSH Launch of va220_vpn on igge.lab.netinsight.se completed in 5 960 ms
[06/10/15 15:29:47] SSH Launch of netsim2_system_regr on igge.lab.netinsight.se completed in 5 965 ms
[06/10/15 15:29:47] SSH Launch of videoaudio_access_ARK_VAM_and_ISM on igge.lab.netinsight.se completed in 5 976 ms
[06/10/15 15:29:47] SSH Launch of videoaudio_access_vam on igge.lab.netinsight.se completed in 5 979 ms
[06/10/15 15:29:47] SSH Launch of eth_10g on igge.lab.netinsight.se completed in 5 981 ms
[06/10/15 15:29:47] SSH Launch of system_regr on igge.lab.netinsight.se completed in 5 992 ms
[06/10/15 15:29:47] SSH Launch of netsim_system_regr on igge.lab.netinsight.se completed in 6 009 ms
[06/10/15 15:29:49] SSH Launch of mutzi on mutzi.netinsight.se completed in 7 499 ms
jun 10, 2015 3:29:49 EM jenkins.InitReactorRunner$1 onAttained
INFO: Loaded all jobs
jun 10, 2015 3:29:49 EM hudson.model.AsyncPeriodicWork$1 run
INFO: Started Download metadata
jun 10, 2015 3:29:49 EM hudson.model.AsyncPeriodicWork$1 run
INFO: Finished Download metadata. 0 ms
jun 10, 2015 3:29:49 EM org.jenkinsci.main.modules.sshd.SSHD start
INFO: Started SSHD at port 51649
jun 10, 2015 3:29:49 EM jenkins.InitReactorRunner$1 onAttained
INFO: Completed initialization
jun 10, 2015 3:29:50 EM org.springframework.web.context.support.StaticWebApplicationContext prepareRefresh
INFO: Refreshing org.springframework.web.context.support.StaticWebApplicationContext@1994aa64: display name [Root WebApplicationContext]; startup date [Wed Jun 10 15:29:50 CEST 2015]; root of context hierarchy
jun 10, 2015 3:29:50 EM org.springframework.web.context.support.StaticWebApplicationContext obtainFreshBeanFactory
INFO: Bean factory for application context [org.springframework.web.context.support.StaticWebApplicationContext@1994aa64]: org.springframework.beans.factory.support.DefaultListableBeanFactory@5c5ba35
jun 10, 2015 3:29:50 EM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@5c5ba35: defining beans [authenticationManager]; root of factory hierarchy
jun 10, 2015 3:29:50 EM org.springframework.web.context.support.StaticWebApplicationContext prepareRefresh
INFO: Refreshing org.springframework.web.context.support.StaticWebApplicationContext@7679d84e: display name [Root WebApplicationContext]; startup date [Wed Jun 10 15:29:50 CEST 2015]; root of context hierarchy
jun 10, 2015 3:29:50 EM org.springframework.web.context.support.StaticWebApplicationContext obtainFreshBeanFactory
INFO: Bean factory for application context [org.springframework.web.context.support.StaticWebApplicationContext@7679d84e]: org.springframework.beans.factory.support.DefaultListableBeanFactory@42caa4ac
jun 10, 2015 3:29:50 EM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@42caa4ac: defining beans [filter,legacy]; root of factory hierarchy
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect TEST
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect common_bist
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect eth_ism
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect eth_n3xx
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect eth_n6xx
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect iptrunk_1G_ism_ark
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect iptrunk_TT
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect iptrunk_compression
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect iptrunk_n390_two_nodes
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect iptrunk_sdh_10g
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect iptrunk_switching_n390
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect netsim_random_50_nodes
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect svanen_system_n360_regr
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect svanen_system_n390_regr
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect va220
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_J2K_1st
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_J2K_2nd
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_access_ARK_MADI
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_access_ISM_DS3E3
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_access_ISM_SDI
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_access_ISM_STM1
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_access_vam_and_J2K_1st
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect videoaudio_sdi4k
jun 10, 2015 3:29:50 EM hudson.slaves.SlaveComputer tryReconnect
INFO: Attempting to reconnect {{ JENKINS_SLAVE }}
[06/10/15 15:29:50] SSH Launch of svanen_system_n360_regr on igge.lab.netinsight.se failed in 9 ms
[06/10/15 15:29:50] SSH Launch of netsim_random_50_nodes on igge.lab.netinsight.se failed in 9 ms
[06/10/15 15:29:50] SSH Launch of videoaudio_access_ISM_SDI on igge.lab.netinsight.se failed in 7 ms
[06/10/15 15:29:50] SSH Launch of svanen_system_n390_regr on igge.lab.netinsight.se failed in 14 ms
[06/10/15 15:29:50] SSH Launch of iptrunk_switching_n390 on igge.lab.netinsight.se failed in 12 ms
[06/10/15 15:29:50] SSH Launch of videoaudio_access_ISM_DS3E3 on igge.lab.netinsight.se failed in 16 ms
[06/10/15 15:29:50] SSH Launch of videoaudio_J2K_2nd on igge.lab.netinsight.se failed in 16 ms
[06/10/15 15:29:50] SSH Launch of va220 on igge.lab.netinsight.se failed in 18 ms
[06/10/15 15:29:50] SSH Launch of videoaudio_J2K_1st on igge.lab.netinsight.se failed in 19 ms
[06/10/15 15:29:50] SSH Launch of {{ JENKINS_SLAVE }} on dummy failed in 18 ms
[06/10/15 15:29:50] SSH Launch of videoaudio_access_ISM_STM1 on igge.lab.netinsight.se failed in 23 ms
[06/10/15 15:29:50] SSH Launch of videoaudio_sdi4k on igge.lab.netinsight.se failed in 23 ms
[06/10/15 15:29:50] SSH Launch of videoaudio_access_ARK_MADI on igge.lab.netinsight.se failed in 37 ms
[06/10/15 15:29:50] SSH Launch of videoaudio_access_vam_and_J2K_1st on igge.lab.netinsight.se failed in 43 ms
jun 10, 2015 3:29:50 EM hudson.WebAppMain$3 run
INFO: Jenkins is fully up and running
[06/10/15 15:29:51] SSH Launch of iptrunk_1G_ism_ark on igge.lab.netinsight.se failed in 958 ms
[06/10/15 15:29:51] SSH Launch of iptrunk_sdh_10g on igge.lab.netinsight.se failed in 978 ms
[06/10/15 15:29:51] SSH Launch of eth_ism on igge.lab.netinsight.se failed in 986 ms
[06/10/15 15:29:51] SSH Launch of eth_n3xx on igge.lab.netinsight.se failed in 989 ms
[06/10/15 15:29:51] SSH Launch of iptrunk_TT on igge.lab.netinsight.se failed in 990 ms
[06/10/15 15:29:51] SSH Launch of TEST on igge.lab.netinsight.se failed in 995 ms
[06/10/15 15:29:53] SSH Launch of iptrunk_n390_two_nodes on igge.lab.netinsight.se completed in 3 523 ms
[06/10/15 15:29:53] SSH Launch of iptrunk_compression on igge.lab.netinsight.se completed in 3 537 ms
[06/10/15 15:29:53] SSH Launch of eth_n6xx on igge.lab.netinsight.se completed in 3 621 ms
[06/10/15 15:29:53] SSH Launch of common_bist on igge.lab.netinsight.se completed in 3 638 ms
jun 10, 2015 3:30:00 EM org.jenkinsci.lib.xtrigger.AbstractTrigger reportError
WARNING: Polling failed
java.lang.NoClassDefFoundError: hudson/matrix/MatrixRun
at org.jenkinsci.lib.envinject.service.EnvInjectActionRetriever.getEnvInjectAction(EnvInjectActionRetriever.java:25)
at org.jenkinsci.lib.envinject.service.EnvVarsResolver.getEnVars(EnvVarsResolver.java:56)
at org.jenkinsci.lib.envinject.service.EnvVarsResolver.getPollingEnvVars(EnvVarsResolver.java:35)
at org.jenkinsci.plugins.urltrigger.URLTrigger.getURLValue(URLTrigger.java:182)
at org.jenkinsci.plugins.urltrigger.URLTrigger.checkIfModifiedEntry(URLTrigger.java:210)
at org.jenkinsci.plugins.urltrigger.URLTrigger.checkIfModified(URLTrigger.java:200)
at org.jenkinsci.lib.xtrigger.AbstractTrigger$Runner.run(AbstractTrigger.java:199)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.ClassNotFoundException: hudson.matrix.MatrixRun
at jenkins.util.AntClassLoader.findClassInComponents(AntClassLoader.java:1376)
at jenkins.util.AntClassLoader.findClass(AntClassLoader.java:1326)
at jenkins.util.AntClassLoader.loadClass(AntClassLoader.java:1079)
at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
... 10 more

Try downgrading the plugins involved in this if you upgraded them today: URLTrigger, XTrigger, env-inject, Matrix project. Or only downgrade Jenkins master itself. If you skipped some versions, try to do a "binary search" for the first broken release.

The goal would be to determine which specific component + version introduced the problem.

I've discovered something important. I can create a copy of a nonworking job. For this new job the URL trigger polling doesn't give any error messages. However, if I run the new job once, it starts to fail URL trigger polling after that. The config.xml files are identical for the two jobs. I also did a "diff -r --brief" of the two jobs directories on the Jenkins server, and the only notable difference was, the new job that was working had no workspace and no builds.

I then:

1. Deleted the workspace => still not OK
2. Deleted all the builds => OK again
3. Build once => not OK
4. Delete the build => OK again (workspace still present)

So the conclusion is that a job with builds cannot poll an URL with URL trigger plugin successfully.

If my last comment gives you anything to go on, please let me know. Otherwise I will start bisecting the versions. I worried about compatibility though. What is the best way to go about? Is there a way to downgrade Jenkins and let it downgrade incompatible plugins automatically?

URLTrigger Plug-in 0.38 is the culprit. Version 0.37 works fine. Tried a lot of other combinations so I'm pretty sure.

I think https://github.com/jenkinsci/urltrigger-plugin/commit/80759be06deff5037ab1ea436ecd694837c5b109 is responsible and commented there.

Fix proposed.

Code changed in jenkins
User: Oliver Gondža
Path:
pom.xml
http://jenkins-ci.org/commit/urltrigger-plugin/7523a42e212d76b8f822bae4acbfaa99262f1c22
Log:
[FIXED JENKINS-28834] Declare dependency on matrix project plugin

Code changed in jenkins
User: Gregory Boissinot
Path:
pom.xml
http://jenkins-ci.org/commit/urltrigger-plugin/302362fa86fe782d1833299a5a8067d858361a58
Log:
Merge pull request #11 from olivergondza/JENKINS-28834

[FIXED JENKINS-28834] Declare dependency on matrix project plugin

Compare: https://github.com/jenkinsci/urltrigger-plugin/compare/a3136c397de3...302362fa86fe