Previously on Youtube I experienced some deletions of comments in computer tech channels. Now, in a go-related channel, I have experienced something new to me: a comment temporarily disappearing for a few days while being on hold for closer reading or moderation by a channel admin. Instead of becoming angry, first one should be patient and wait to see whether a comment is permanently deleted or only temporarily hidden.

I think youtube has both automatic detection and user reporting for various types of unwanted comments. They also allow the channel owner to review (some of ?) these comments. Maybe the owner can also remove any comment for whatever reason, I'm not sure, I'm a passive consumer of youtube.

I'll add that some people who put videos on youtube might not care to review comments that are on hold (or lack time and energy to do so). Others clearly care way too much about what is going on in their comment section.

Indeed, many people have seen their comments disappear randomly.

Off-topic:

I recently had a different experience:

Years ago, YouTube stopped notifying me when someone liked one of my comments. This change was not unwelcome.

Last week, I suddenly got notices that someone had liked two of my comments. One of them was for a comment I made years ago. But, it said my comment was made a month ago. In January, someone converted the video to a short. My guess is comments and reactions were ported from the old video to the short.

I guess it's better than having the whole comment section turn into a toxic wasteland.