EDIT: FIXED - Thanks to a helpful Discord user, it turns out this was a setting on Lemmy not on Sync. On lemmy.world settings I had 'show read posts' unchecked. I presume that's default unless I ticked it by accident. Whoops. I'll leave this post up incase it helps anyone else though.

If I read a post, it gets hidden (after a page refresh)

I can't find any way to disable that setting and I really hate it, because I like to revisit threads to check comments on occasion. Does anyone know how to do this?