Cant unmerge some issues that had been previously merged

[cobyeastwood183]

Environment

SaaS (https://sentry.io/)

Steps to Reproduce

There seems to be issues that cannot be unmerged in issues/{groupId}/merged view. All I get is "already being merged". Only appears to happen when issues appear inside issues{groupId}/merged view that are not associated with the same groupId therefore a grouphash record cannot be found.

Expected Result

Should be able to unmerge all issues.

Actual Result

Cant unmerge all issues. Some show as "already being merged".

Product Area

Unknown

Link

No response

DSN

No response

Version

No response

[getsantry]

Routing to @getsentry/product-owners-issues for triage ⏲️

[cobyeastwood183]

Related: #60626

[cobyeastwood183]

https://sentry.zendesk.com/agent/tickets/148511

[lobsterkatie]

I looked into this a bit, and we seem to have some unmergings where the group id for the hash got changed but the process either got stuck or got killed before the new group id could be applied to the events in that issue. So because of the events, the hash shows up on the merged issues tab for the old group, but because the hash has already been moved to the new group, we come up empty when looking for the hash in the old group, which is what leads to the "already being unmerged" error. Note that unlike in the issue linked in the comment above, the hash isn't stuck in an unmerging state - it's fully unmerged, it just didn't manage to take its events with it.

It's not clear how this happens, but it may take some manual intervention to fix (or for the events to age out, since new events with the hash in question will go correctly into the new group).

One thing we might consider is linking the related Activity records or otherwise keeping track of unmerges in GroupHashMetadata, just as a way of giving us more information for debugging.