Another update and possibly a solution for some case where posts were not properly deleted. Seems I jumped the gun on this and the restores haven't been intentional - at least not in this particular case.
There is a limitation in the popular Powerdelete that apparently prevents mass editing. Here is a link to a new version with a build-in delay and some other alternatives:
There are other reported cases where manually deleted post reappeared or other scripts have been used, so this doesn't solve all issues but explains how posts that were both edited and deleted withPowerdelete weren't properly deleted and reappeared after subs went back live.
Update: As some have pointed out: the restores can be rollbacks from the server issues or post haven't been properly deleted due to subs being private during blackouts. Many have experienced the same issue, I can't explain how this happens. I'll just run the script again, try the GDPR request and delete my account.
Also worth noting: according to the ToS Reddit can actually do whatever they want with existing content, apparently we agreed to this when signing up.