Clicking 'show more comments' removes ability to 'reply to comment'

I can't see what you mean, do you have screenshots of the behaviour?

I can confirm this. Clicking the "Show $$anonymous$$ore Comments" button removes the little "reply" icon that shows up when you hover your mouse next to a comment's header. It's usually to the right of the vote up and vote down buttons, and to the left of share, but it's gone if you click show more comments in OP's link.

It only tends to disappear for me if the comment is already nested a few times.