A thread with 20 of your posts doesn't have to be deleted to see this. The number of posts may be displayed incorrectly, recounts are made from time to time. There are plenty of threads about this issue.
Thanks for the links. If there was a big recount, then apparently this is a very rare occurrence, because in almost 4 years of my active presence on the forum, for the first time I encountered such phenomena that a bunch of posts simply disappeared. Although I have not rarely observed such moments when the counter suddenly became less by 1 or 2 posts. I usually attributed such moments to moderation, because I know that notifications do not always come. I see the correction of my counter immediately for 20 posts for the first time.