I only managed to reproduce this once, after that, it's running smooth. But I have a theory.
The save is failing, because it fails to commit to GitLab.com, which seems to be a timeout issue in their end. I am not too happy about the GitLab integration. I like the idea, but there are a few things that really didn't turn out as intended.
I would like to wait for a few days to see what happens in their end. Otherwise I might have to remove the integration between the sites.