Merging gitlab MR puts commits to unsynced state and they are lost from the master branch

We’re using subgit installed right on the gitlab server to bidirectionally mirror changes between svn and git.

Sometimes, when we merge a MR via the gitlab, the changes are get lost from the master branch.

Looking at the logs we see that commit got to the unsynced state.

[2023-03-20 12:09:17.075][daemon][29] Creating backup for unsynced commits: 5f55e21ee7d38413bdebeaf7b775e1de95a38a03 initially referred by refs/heads/master and now stored at refs/subgit/unsynced/heads/master/2
[2023-03-20 12:09:17.099][daemon][29] Reset the following refs because they were non-fast-forward updated: [refs/heads/master]
[2023-03-20 12:09:17.099][daemon][29] Restoring refs to reflect SVN state.
[2023-03-20 12:09:17.112][daemon][29] Refs were successfully updated

I didn’t manage to find any information in regards to unsynced commits, when do they happen and how to fix them.

I saw the instructions appearing on how to fix the unsynced commit when you push from the console. But if we use GitLab that just silently gets lost.

What options do we have to make it work? At least block MR merging from the gitlab side to manually resolve any conflicts.