This is an old post but if you get in here maybe your are having problem where one (or more) tag is not listed while creating a new topic. I had the same problem, here is the post about it, comments, diagnostic and solution. Check this link: https://meta.discourse.org/t/user-cannot-create-a-new-topic-and-tag-it-during-creation-the-tags-are-not-listed/366318/1