I used a rust port of shreddit to delete all my posts across all my accounts, such that when logged in, there are no posts on my profile, however, I spent about a month on and off googling my username and finding posts that didn't stay deleted but wouldn't show up on my profile.

So I'd guess that reddit somehow restored some number of posts, and it seems to occasionally continue to do so.

In terms of hurting the site, it absolutely does. Reddit is a ghost town, and I find deleted posts constantly that google thinks are relevant. It's a shame it had to be this way.