Yes, weirdly enough at the time there was no reply button, I thought HN comments had a maximum nested depth, but now it has a reply button and so does yours. Weird.
Ah, no worries! Replies seem to get throttled sometimes when the site detects a lot of nested replies quickly and it intentionally delays the ability to reply a bit. I've always assumed that it's intended as a way to try to mitigate threads that potentially are devolving into flamewars.