To be clear, you see the spam when logged in, then don't see it logged out, then see it again when logged in again?
Correct.
Or, I can do it if you don't feel like it and don't mind me using your screenshots
I haven't used codeberg yet, so I'll just say sure you can use my screenshots/words. It also directly affects you as a mod more as you've said, anyway.
Using those usernames/profiles to look at the posts directly, I don't suppose there is anything that might detail what is going on? There are ~500 open issues, maybe this is some existing database/caching issue possibly related to post/community IDs? Though I am still not sure why viewing would differ by user.