Somewhat related, Reddit has been broken for me in a very similar way for more than a year now. Whenever I scroll down to load more pages, it will populate with about 80% the same threads as it loaded on previous pages. Over and over, such that by the time I’m on page 6 or so, I will have 6 of the exact same thread.

Really stupid bug that probably only happens with old.Reddit or RES or something. But it’s nice in that it keeps me off of Reddit I guess.

Common bug for caching lists that are reordering all the time.

Unlikely to be fixed though since it causes you to very quickly skip the repeat content (without having to serve you more than headlines) and see more ads. The "bug" multiplies the value they can get from each post which is a very important metric especially as llm slop has started to destroy perceived value from random posts from strangers (reddits only resource).

I'm not saying they introduced it on purpose the way Google intentionally showed bad search results to encourage a second query but I'm not confident that fixing it will be high on the priority list until it makes people leave the site.

I can confirm that that bug exists even on "new" Reddit.