Same issue as https://issues.jenkins.io/browse/JENKINS-57097

but Im using Gitlab.

The first time I create the multi-branch pipeline and scan the repo Jenkins retrieves the correct Jenkinsfile. But when I amend the commit and push, the next scan will continue to use the Jenkinsfile from the old commit:

Verifying host key using known hosts file, will automatically accept unseen keys
 > "C:\Program Files\Git\bin\git.exe" fetch --tags --force --progress --prune -- origin +refs/heads/*:refs/remotes/origin/* # timeout=10
Checking tags...
  Checking tag 2.2.15
      ‘Jenkinsfile’ found
    Met criteria
Changes detected: 2.2.15 (null → f21197535346b4278d8466abed6b0b88a104bee9)

Where "f21197535346b4278d8466abed6b0b88a104bee9" is the old commit.

In the old pipeline plugin there was a way to provide a custom Jenkinsfile in the config, but in multi-branch pipeline plugin the only Build Configuration > Mode is by Jenkinsfile with a path. So Im completely stuck. I cant setup a build job where I cant change the Jenkinsfile.