CI build pending with Gitlab Merge Request Builder Plugin

I use GitLab 8.7.3 and Jenkins 2.3 with Gitlab Merge Request Builder Plugin 2.0.0

Until before, when we made merge-request on gitlab, Jenkins build is started and Jenkins put a comment Build PASS or Failed.

But now, there "CI build pending" without jenkins comments on merge-request

I find the following log in Jenkins:

WARNING: org.jenkinsci.plugins.gitlab.GitlabBuildTrigger.run() failed for hudson.model.FreeStyleProject@b0ec9[Project_name]
java.lang.NullPointerException
    at org.jenkinsci.plugins.gitlab.GitlabMergeRequestWrapper.check(GitlabMergeRequestWrapper.java:100)
    at org.jenkinsci.plugins.gitlab.GitlabRepository.check(GitlabRepository.java:86)
    at org.jenkinsci.plugins.gitlab.GitlabRepository.check(GitlabRepository.java:68)
    at org.jenkinsci.plugins.gitlab.GitlabMergeRequestBuilder.run(GitlabMergeRequestBuilder.java:28)
    at org.jenkinsci.plugins.gitlab.GitlabBuildTrigger.run(GitlabBuildTrigger.java:134)
    at hudson.triggers.Trigger.checkTriggers(Trigger.java:273)
    at hudson.triggers.Trigger$Cron.doRun(Trigger.java:222)
    at hudson.triggers.SafeTimerTask.run(SafeTimerTask.java:50)
    at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
    at java.util.concurrent.FutureTask.runAndReset(Unknown Source)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(Unknown Source)
    at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)

anyone know how to fix this problem? anyhelp is welcome. Thank you.

why this occurs is that I have built other Jenkins for backup. I didn't notice it set Crontab to fetch merge-request notification and the Jenkins on backup server couldn't build due to another reason.

Thank you all who read or thought this issue.