I like to check my posts to see if there's any interesting replies, I do this through the "find latest posts" option in my profile but I've noticed fairly often that there's some threads I remember having posted in that are missing from the search results. there doesn't seem to be any pattern to it either
the threads still exist, can be found by regular forum navigation and my posts are still there inside them. they'll usually show up again later. but for a while the search just doesn't seem to find them