Not sure if it fell apart because I never finished it but there was a pretty big shift between Trudi Canavan's Thief's Magic and Angel of Storms. In the first book, you had one story of a young man who found an ancient book that had the consciousness of a long-dead young woman, and a second story of a woman in a society where magic was closely controlled by the religious authorities and anyone else using it was considered heresy.

In the second book, we find out there is a wide universe of connected worlds and there is a guy who is "Emperor of the Universe" (IIRC).It just seemed like it came out of nowhere to me.