Google Books: EPub book covers not appearing

Google to the rescue!

Being the owner of various OSs, its always a joy to have apps that sync data across multiple platforms. Google finally gave me that with its newest update.

Unfortunely, its not perfect.

For some reason, some of my ePub and PDFs are not generating covers for their books.

Is anyone who is using this app or trying it out experiencing the same thing? Possible fixes?