relevant issue in kbin's issue tracker https://codeberg.org/Kbin/kbin-core/issues/649
Edit: It is a bit strange that post specifically was in a code block, but it appears to be on lemmy's side as well. I'm trying to think, there are a few renderer issues with 0.18.3 so maybe something happened there if the OP did not intend to put it in one
Recently I noticed with another user that they had blocked a domain and it, for some reason, was hiding all comments in the thread despite the blocked domain being completely unrelated to the post (the post wasn't on that domain, wasn't by someone on that domain, and no commenters were from that domain).
If posts are disappearing when you're logged in but not when logged out, it should be something like that: either a language filter, federation turned off, or a blocked community you might not expect filtering it out. You can double check by unblocking domains/magazines to see if any of them return comments, though that might be troublesome with many blocked.