What happened to book four?

Basically Wiz had some personal issues and was on medication as a result, this medication changed Wiz's writing style about half way through book three and when he got off the medication Wiz decided to rewrite large parts of book three in order to fit it with his vision of the series. This naturally pushed back book four's release date significantly and whilst we should expect to see book three sometime soon (in the next few months) book four is probably a bust for this year.

You can read the full run down in this post on his facebook: WARNING MINOR BOOK THREE SPOILERS https://www.facebook.com/AuthorKerr/posts/348879946538786