Yeah, it's an issue with the latest Lemmy version. We had a bit of a chat about it in the Lemmy.nz Matrix chat room. Seems to be that the database optimisations have caused comments to come in a different order than the website side is expecting, so I guess it fails to contruct them on the page.

Unfortunately rolling back the server probably isn't possible, because of the database changes. At the very least it's risky. Might be better to use an app, or another frontend like old.lemmy.nz or voyager.lemmy.nz as hopefully they aren't affected.

I'm closely monitoring the bug report waiting for the fix, but it seems at the moment every release it's two steps forward, one step back.