Maybe you got the answer already but I want to still give an answer to the context of the title.

If your thread is not in the board where you have created it then its possibly don't fit into the board for example you are asking a forum related question in beginners section so don't be surprised if you refresh this page and you will find the topic in Meta.

Sometimes it will be deleted by mod if its a spam/no value/troll or violates any of the forum rules and you wilk get the notification about deleted posts in PM.