GitLab not updating branch when MR accepted

GitLab is able to accept MRs but sometimes under heavy load, the MR shows it’s been merged while the branch actually is not updated. This happens several times when the GitLab load is heavy.
The MR shows up as being merged so I can’t close it and reopen it. Users now have to re-push the commit over again when this happens.

Would like to know a command or a way to just update the branch when this happens.