Anyone who has used Reddit for any period of time (or basically any similar site, which includes FB, Twitter, and even HN), has seen data consistency issues during high load (like periods of activism). Shards die or fall out of quorum, work queues get purged, etc. That's the reality of systems with a lot of very low value data.
Eventually consistent, but also perpetually inconsistent.
No database shard would ever have been left that far out of date due to high load.
The only Hanlon's razor I can imagine here is somebody wrote a query to try to undelete something small (intending a single user or something) and forgot the WHERE clause and started to undelete everything. And didn't realize until the query had been executing for several minutes.
Yikes.
(I do actually think this is the most likely, not because of spez's motivations, but because there's zero benefit for Reddit here. It might make sense for them to force subreddits back to public, but undeleting old comments has no strategic value right now.)
The obvious benefit would be to artificially keep interaction rates high by "grave robbing" old comments and accounts.
"Nobody is ever going to notice, those accounts are long dead!"
The metrics you use to attract investment are things like monthly active users, and whether a comment was deleted after it was made doesn't affect that at all.
People are going back to revisit things they think they deleted a long time ago to find it not deleted.
It's possible that those items were deleted, and then suddenly undeleted over the past few days as Reddit plies its nefarious plans. Far more likely, they were never deleted in the first place, or had the same temporal issue and reappeared a short while after deletion, but long long ago. The person thought it was deleted, but it wasn't for the same reason people are finding deletes not to stick now in some cases.
It's still possible that this is innocent(ish), but at low enough probability that malice really does seem like a compelling alternative explanation. After all, spez has been caught doing something very similar before. There's proof of malicious nature, not just an assumption. When a component in a system has a certain known behavior or limit, you don't just discard that knowledge due to some handy rule of thumb.
(Of course this is assuming pushsift has gotten the majority of comments)
The more posts we see deleted the less likely it is that it's an accident. I just checked and found out that posts from an account that I scrubbed and deleted 5 years ago are popping back up. That stretches "eventual" pretty thin.
We also have a large amount of external information that suggests that reddit is not acting in good faith, much of it from Spez himself.
Between the two of those, malice is more likely than stupidity to be the motivating factor.
I care more about what a 'deleted' post says, than any other post in a thread. I imagine there is a good reason for that.
Of course this isn't "heavily regulated". No law demands 100% consistency when you run some third party script during an outage. Clicking "delete" on a comment, or having a script do it, is not some GPDR enforced action.