Similar to the thing yesterday, we have a user who doesn't seem to be able to merge despite sync/restacks with an even less meangingful message:

GitHub had a critical incident affecting pull request creation (*https://stspg.io/sm1tp7kfm4vj*), and their own update at 19:40 UTC said they were "investigating errors creating pull requests." Our merge queue creates a draft PR as part of merging, and GitHub returned a 500 with an empty response body on that call, which is why the message came back as "unknown reason" with no detail — there was literally no error text for us to show you. Your PR got squashed and rebased fine; it only fell over on that last GitHub call. GitHub resolved the incident at 20:23 UTC, so re-queueing #13117 should merge cleanly now.

if the message said like "unknown error: github returned 500 creating pull", or "issue with git provider" or some better words, probably would have caused me to check github status even though github didnt return a why. looks to be working now like you said , Thanks!

Agreed here, I have spun up a note on this for the team. Its a failsafe when we don't get an error back from GitHub but we can do a better job here. No ETA when this might be implemented.