Board Thread:Online Discussion/@comment-27045852-20151005003158/@comment-3076045-20151005092542

The next main quest won't become available until you are the required level.

For example, if you've completed the quest to rescue Lyris, the following quest (Castle of the Worm) won't become available until you are level 20.

It may be a case of that as to why it's not appearing yet.