I have now disabled the use of GitLab.com, it won't be updated with the latest versions of the files anymore.
The main reason is that their API started to respond with HTTP 500 whenever updating script 528. Formerly I have had similar issues where a whole repository didn't work. I am starting to lose confidence in their product.
I also noticed that all changes made on GitLab.com created Merge Requests. I never checked if "developers" could merge them, but just missed that they should do it. I have merged all there was, but with a quite long response time. According to the permission roles, it looks like you should have been able to merge as well.
I have demoted everyone but myself to role Guest instead of Developer while GitLab isn't in use. Since it will be out of sync, it makes no sense to update anything there.