Merging to branch failing with unhelpful message 'An error occurred while merging. Try again.'

When attempting to merge my branch into another branch, after selecting the merge button after obtaining approvals i consistently get the error message 'An error occurred while merging. Try again.' Tried creating a new MR and branch and got the same issue. Not seeing any additional error information.

Proposal

Based on information from #439946 (comment 1887805299), it seems like there might be failure reasons here. We should include the failure reason to make the message more helpful. While it won't solve the issue for users being able to merge, they'll at least know why.