and am seeing the same issue. deleting the root comment removes the entire comment chain. i didn’t notice it at first because (i’m assuming) i’m an admin and can see deleted posts/comments, but when I checked it when not logged in the entire comment chain was indeed gone. and once i un-deleted the comment it was back.
i then deleted a non-root comment, and now it behaves even differently, with a link saying “2 more replies” but when you click on it it just spins forever. will check to see if there’s already a bug related to this issue and report back.