Branches being disabled in multi branch pipelines since update to Gitlab 13.12.4

### Version report
**Jenkins version:**
[Dev] Jenkins 2.289.1
[Prod] Jenkins 2.263.4
**GitlabBranchSource**: 1.5.1
**GitlabPlugin**: 1.5.20

Last week we updated updated our Gitlab to **13.12.4** and since then have seen on our prod jenkins that the jobs we have defined as multi branch pipelines are not always discovering correctly

We current have it configured for **"master, release*"** and intermittetly during the days they're disabled as the discovery fails.
Trigger of **"Scan Gitlab Project Now"** corrects it will then at some point again revert to disabled

We saw the open pull request #145 and tried building the plugin ourselves based on 1.5.1 with the fix suggested there -> problem persisted
We then buildt based on 1.5.7 with the fix suggested there -> problem persisted

Seems the pull request suggested was based on https://gitlab.com/gitlab-org/gitlab/-/issues/333548

At the moment the only option we have without a fix is to roll back our gitlab version