For jenkins job is configured pipeline.

There are stable connection and all works but,

SOMETIMES without visible reason gitlab webhook does not start (trigger) jenkins job. 

Bug was reproduced when this job is already running and after more than hour of inactivity (it also passed more than 1 hour from last commit to git - as trigger to job). 

Gitlab does not repeated this trigger which means that gitlab received accept ("200") from jenkins server OR does not send webhook at all. 

Detail of process flow is on attached screen.

example: 

first commit - 98a913 - 18.39 28.03.2018 - trigger OK

second commit - 02ebc1 - 12.49 29.03.2018 - no webhook

third commit - be8d57 - 13.40 29.03.2018 - no webhook

fourth commit - 87ea5d - 29.03.2018 - trigger OK

Job is configured to starts on every changes to source or target branches. 

These commits are commits to source branch. 

(looks like https://issues.jenkins-ci.org/browse/JENKINS-34727 with little difference but not depends on time)

***

addition:

received in jenkins log next note with such situation (webhook received, job did not start):

Apr 02, 2018 5:39:18 PM INFO com.dabsquared.gitlabjenkins.webhook.GitLabWebHook getDynamic
WebHook called with url: /project/autograder_main_FeatureBranchBuild
Apr 02, 2018 5:39:40 PM INFO org.eclipse.jetty.server.session.Session beginInvalidate
Session node01use5jw2vbywv16e45jtsmcxcc2420 already being invalidated