The most common reason why your post has "disappeared" is because the server never received it in the first place. If you click on "Post" and there's a network problem or something, you may think it went through, and it didn't. The only way to check the server got your post is to go to the thread after you've posted to it, and make sure your reply is there. If it's not, try posting again.

We don't remove posts randomly.

DocJohn