Following is my original post and an update:
I know there are several threads here about YouTube but here's yet another problem to add to the list, sadly. As of today (latest version of the YouTube app) I'm not seeing any replies under comments except for my own, even when I know there are replies. VoiceOver announces the number of replies for a comment when you touch that comment. I touch a comment and VoiceOver announces that there are 19 replies, yet when I use the View Replies roter action to see those replies, I only see my own reply, or if I haven't replied to that thread, I see none at all.
After posting this I did a bit more experimentation and this just gets even weirder. I have several different YouTube accounts so I tried a couple of them as well as signing out completely and I observe the same behavior, but not on every video nor every comment. Furthermore, and probably pushing this away from being an apple related issue at all, I even tried on my chrome browser on my PC and got the same bizarre results. There’s no rhyme or reason to it. Sometimes I can see some replies, other times none. For example, one comment was supposed to contain 10 replies but when I looked at them, I only saw four. I know YouTube is having a major issue right now with aggressive spam bots so maybe somethings going on on their end.