And guess what happened at that point. nobody saw any of my comments from that point forward, because I was below reading threshold, which meant also that my karma was stuck (I think it was -4). I checked, by logging off and looking for my own comments. I fixed the problem by creating a new account, which gained karma steadily.

I'm pretty sure the comment-visibility rules are different depending whether you're logged in or not. The reason for that is because the logged-out view is what search engines see, so it's especially important to keep bot-produced spam hidden there. Logged-in users have a configurable, per-comment threshold.