The forum system is deleting posts, it happened to me twice after making an edit or two. The post is published, you edit it, after hitting “save” the input fields go empty and the published post disappears. The anti-duplicate mechanism prevents reposting the same content right away, so the posts still have to be somewhere.
You’re topics are being marked as spam. This can happen when you too quickly edit a post and submit. After you’re post is marked as spam until someone fixes it all of your posts will be marked as spam.