When your books aren't loading, the cause is usually either your network connection or your storage.
Try switching between WiFi and cellular data, or try switching from one WiFi network to another WiFi network.
Go to the "More" section of the app and choose to free up storage. Check out how to do that here: Free up storage
If neither of those steps work for you, please reach out to us with your user ID, the name of the book affected, and the specific error code you are receiving.
We will help out as soon as possible!