the delay is real

Can you try with the latest master branch to get https://github.com/jenkinsci/pipeline-maven-plugin/commit/a94794456c1a6bb6342729f41569418e1e4cbf31
You will have a log message "[withMaven] triggerDownstreamPipelines completed in xxx ms" if the duration is greater than 5 seconds or if you enable logs on org.jenkinsci.plugins.pipeline.maven.listeners.DownstreamPipelineTriggerRunListener .

Can you please also generate few thread dump during the processing? With jstack or with Jenkins URL /threadDump

dantran I have aggregated all the maven artifacts into one single upstream cause to support a relationship on many artifacts.

https://github.com/jenkinsci/pipeline-maven-plugin/tree/JENKINS-53392

i am currently running private build which has this commit  https://github.com/jenkinsci/pipeline-maven-plugin/commit/a94794456c1a6bb6342729f41569418e1e4cbf31 to get teh timeout logger.

The delay varies 5 to 40 mins.  I also have the thread dump while delay is going on.  Need to digest the output

Will try latest build for JENKINS-53392

dantran can you please try with https://github.com/jenkinsci/pipeline-maven-plugin/releases/tag/pipeline-maven-3.5.12-beta-3 ?
It's the beta release than contains JENKINS-53392

I deployed the latest from source. Upstream jobs did not come to complete after 40 minutes ( ie any ending logger about triggering).  I ended up to revert  back to 3.5.9

The interesting is the double downstream trigger issue was there all along.  

Thought of reverting changes at 3.5.10 where problem started?

there was a performance regression that was very visible in your special case with so many generated maven artifacts being dependencies on the downstream pipeline.

 Can you please test with the latest https://github.com/jenkinsci/pipeline-maven-plugin/tree/JENKINS-53396 (I have amended a commit to add a troubleshooting log message).
1. Enable logging "org.jenkinsci.plugins.pipeline.maven.listeners.DownstreamPipelineTriggerRunListener=FINEST"
2. Launch your upstream job
3. You will see "299 times" in the build logs a troubleshooting message that will look like

[withMaven - DownstreamPipelineTriggerRunListener] Skip eligibility check of pipeline dependency-graph/my-downstream-of-a-multi-jar-project/master for artifact com.example.multi-jar:jar-2:jar:0.0.1-SNAPSHOT(0.0.1-20180903.201513-17), eligibility already confirmed

Reference: https://issues.jenkins-ci.org/browse/JENKINS-53396

2018-09-03 22:55 CEST: code merged in master branch

confirm!!! installing latest from source works for me.  I can see the mentioned loggers.  Looks like we finally got the closure. The delay time is within 30sec consistently.

Thank you.

Tested with 3.5.12-beta-4

3.5.12