I am using Github Organization to manage my Jenkins projects. I keep getting reports about Jenkins not picking up jobs for push events.  I did notice that every time I scanned the repo everything was picked up just fine but for some reason web hooks were failing. I check the failing projects Repository Events and found all branches with # in the name were causing events to fail. 

Here is a trace from a test I created:

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[Fri Sep 15 14:22:29 UTC 2017] Received Push event to branch feature/#JenkinsTest in repository XXXXXXXX/XXXXXXXXXX CREATED event from ⇒ https://XXXXXX.XXXXXXX.XXX/github-webhook/ with timestamp Fri Sep 15 14:22:24 UTC 2017
[Fri Sep 15 14:22:29 UTC 2017] Received Push event to branch feature/#JenkinsTest in repository XXXXXXXX/XXXXXXXXXX CREATED event from ⇒ https://XXXXX.XXXXXXX.XXX/github-webhook/ with timestamp Fri Sep 15 14:22:24 UTC 2017
Examining XXXXXXXX/XXXXXXXXXX

Checking branches...

Getting remote branch feature/#JenkinsTest...
ERROR:

{"message":"Branch not found","documentation_url":"https://developer.github.com/v3/repos/#get-branch"}

java.io.FileNotFoundException: https://api.github.com/repos/XXXXXXXX/XXXXXXXXXX/branches/feature/#JenkinsTest
at com.squareup.okhttp.internal.huc.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:243)
at com.squareup.okhttp.internal.huc.DelegatingHttpsURLConnection.getInputStream(DelegatingHttpsURLConnection.java:210)
at com.squareup.okhttp.internal.huc.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:25)
at org.kohsuke.github.Requester.parse(Requester.java:602)
at org.kohsuke.github.Requester.parse(Requester.java:584)
at org.kohsuke.github.Requester._to(Requester.java:264)
Caused: java.io.FileNotFoundException:

{"message":"Branch not found","documentation_url":"https://developer.github.com/v3/repos/#get-branch"}

at org.kohsuke.github.Requester.handleApiError(Requester.java:660)
at org.kohsuke.github.Requester._to(Requester.java:285)
at org.kohsuke.github.Requester.to(Requester.java:226)
at org.kohsuke.github.GHRepository.getBranch(GHRepository.java:1234)
at org.jenkinsci.plugins.github_branch_source.GitHubSCMSource$LazyBranches.create(GitHubSCMSource.java:1773)
at org.jenkinsci.plugins.github_branch_source.LazyIterable.iterator(LazyIterable.java:57)
at org.jenkinsci.plugins.github_branch_source.GitHubSCMSource.retrieve(GitHubSCMSource.java:869)
at jenkins.scm.api.SCMSource._retrieve(SCMSource.java:355)
at jenkins.scm.api.SCMSource.fetch(SCMSource.java:309)
at jenkins.branch.MultiBranchProject$SCMEventListenerImpl.processHeadCreate(MultiBranchProject.java:1300)
at jenkins.branch.MultiBranchProject$SCMEventListenerImpl.onSCMHeadEvent(MultiBranchProject.java:1134)
at jenkins.scm.api.SCMHeadEvent$DispatcherImpl.fire(SCMHeadEvent.java:247)
at jenkins.scm.api.SCMHeadEvent$DispatcherImpl.fire(SCMHeadEvent.java:230)
at jenkins.scm.api.SCMEvent$Dispatcher.run(SCMEvent.java:481)
at jenkins.security.ImpersonatingScheduledExecutorService$1.run(ImpersonatingScheduledExecutorService.java:58)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201(ScheduledThreadPoolExecutor.java:180)
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:293)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
at java.lang.Thread.run(Thread.java:748)
[Fri Sep 15 14:22:30 UTC 2017] Push event to branch feature/#JenkinsTest in repository XXXXXXXX/XXXXXXXXXX CREATED event from ⇒ https://XXXXX.XXXXXXX.XXX/github-webhook/ with timestamp Fri Sep 15 14:22:24 UTC 2017 processed in 0.34 sec