I hate a lot of the things that reddit has been doing but I still think not all of them are on purpose. I ran into this issue myself before it was widely discussed and my first thought was that it had simply failed to delete some comments or deleted only from some cache.

So far every exampe I’ve seen of this can still be explained by bad engineering and I see no reason to think it is “undeleting” stuff by design, since it seems to happen to very random content that has no general value (like restoring 20 random comments out of 900 that were deleted).

There was a post somewhere here on lemmy recently that inspired an idea for something like this:

An ultimate AI dominated the world and kept humans only on zoos along with all other animals. Over several generations those humans lost all knowledge and culture they had. Eventually the AI got wiped out by some natural disaster and it allowed humans to start over.