What phone, OS version, and app version are you using? Amazon will need to know that info in your email. You might also try to uninstall and reinstall the app. IDK if you can backup the books to your Amazon account, but if you can, do so before uninstalling.
Try clearing out the cache for the app. Given this is a preinstalled app, you might not be able to uninstall the app. Contacting Amazon for updated information regarding the update to the OS on your phone might be helpful considering they created and maintain the app and it's updates and compatibilities with OSs.