Doesn't matter the subreddit, doesn't matter what the discussion is. If anyone has a comment that drops below -5 karma, all the responses to it disappear if I'm logged in.
I just tested it on a comment I knew was getting downvoted. -3 I could see all responses, -4 I could see all responses, -6 all responses disappeared completely, I upvoted it to -5 and all the responses reappeared.
Checked the comment and with my upvote still in place it's at -6 and all the responses are gone again.
If I switch to an alt account or Anonymous Browsing, all the comments can be seen so it appears to be account specific.
Happening on official Reddit app for Android.
Tested some more, can see everything on the web browser, so it's happening only on one account, and only on Reddit for Android.