Error code 500 when push events triggered from a GitLab project

We are having a Multibranch pipeline job in Jenkins to trigger CI when a new branch is created in a project or any new merge request is created and merge accepted (after merged). For this, we are maintaining two hooks.

  1. System hook
  2. Pull request hook.

As far as checked, there are no issues with hooks seems.

For the past 2 days, we are getting the "There is some unexpected error in jenkins-api. Please try again :-(" exception as a comment in Merge Request created. It is because the indexing for the multi-branch pipeline job is not run and so, the job for the new branch is not created in Jenkins and causing the exception when CI triggers for the new merge request given.

When I try to test the push event for the hook (http://jenkins.com:8080/project/Test/Test2-mobile-samples) from GitLab, i got the below error.

image

If you need any other details, please let us know. We will share the required details ASAP and it is very urgent for us to fix this issue.