The branch indexing detects successfully all MRs and branches. But never starts the pipeline.

It only tells  ‘Jenkinsfile’ found but is a directory not a file. It seems the checkout/lightweight checkout does not work. The above message shows up always. Regardless the auth method is ssh or https. Even if I enter a wrong password it fails with same error messages. In the jnkins system log there is an exceptions from the gitlab api.

Here some logs:

"

Started
[Tue Aug 18 13:58:56 CEST 2020] Starting branch indexing...

Unable to detect if it is a mirror or not still fetching MRs anyway...

Checking branches..

Checking branch master
      ‘Jenkinsfile’ found but is a directory not a file
Does not meet criteria

Checking branch test_branch

Checking branch test_branch_2

3 branches were processed

Checking merge requests..

Checking merge request !5
      ‘Jenkinsfile’ found but is a directory not a file
Does not meet criteria

Checking merge request !4
      ‘Jenkinsfile’ found but is a directory not a file
Does not meet criteria

2 merge requests were processed
[Tue Aug 18 13:58:58 CEST 2020] Finished branch indexing. Indexing took 2 sec
Finished: SUCCESS

"

System log:

"
Aug 18, 2020 2:14:56 PM WARNING io.jenkins.plugins.gitlabbranchsource.GitLabSCMSource getMembers
Exception while fetching membersorg.gitlab4j.api.GitLabApiException: user_id is invalid org.gitlab4j.api.GitLabApiException: user_id is invalid at org.gitlab4j.api.AbstractApi.validate(AbstractApi.java:633) at org.gitlab4j.api.AbstractApi.get(AbstractApi.java:213) at org.gitlab4j.api.Pager.<init>(Pager.java:92) at org.gitlab4j.api.ProjectApi.getAllMembers(ProjectApi.java:1411) at org.gitlab4j.api.ProjectApi.getAllMembers(ProjectApi.java:1372) at io.jenkins.plugins.gitlabbranchsource.GitLabSCMSource.getMembers(GitLabSCMSource.java:219) at io.jenkins.plugins.gitlabbranchsource.GitLabSCMSource.retrieve(GitLabSCMSource.java:316) at jenkins.scm.api.SCMSource._retrieve(SCMSource.java:373) at jenkins.scm.api.SCMSource.fetch(SCMSource.java:283) at jenkins.branch.MultiBranchProject.computeChildren(MultiBranchProject.java:641) at com.cloudbees.hudson.plugins.folder.computed.ComputedFolder.updateChildren(ComputedFolder.java:278) at com.cloudbees.hudson.plugins.folder.computed.FolderComputation.run(FolderComputation.java:165) at jenkins.branch.MultiBranchProject$BranchIndexing.run(MultiBranchProject.java:1032) at hudson.model.ResourceController.execute(ResourceController.java:97) at hudson.model.Executor.run(Executor.java:428)

"