It really doesn’t matter much to the user how many comments are going to be loaded next in my opinion, and that keeps it simple on our end.
Here's what trips me up: even if I don't display the number, I still need to know whether extra comments can be loaded on that depth. If not I don't want to display a "Load more". You could of course let the "Load more" load hidden comments at any level of that subtree, but I think that causes unexpected behavior.
Maybe this clarifies what I'm talking about:
In the case on the right, there's an unexpected downward shift of content which may disorient the user.
Interesting! If there are two deleted comments underneath 2157873, that could indeed explain the two "missing" comments.