Kindle Fire looses books - solution
This is how I restored all my missing books, docs, news & music that had been downloaded by both Amazon cloud and calibre. Using root explorer I could see that they were on the Kindle.
This appears to be a problem with rooted Kindles getting the Kindle Android app installed. This is what worked on our two Kindles.
From the Home screen:
* Settings (gear icon) > More...> Applications
* Set filter to "All Applications"
* Swipe down to the Amazon Kindle App
* Clear Data
Hard reboot; press the on button until you get the shutdown message, shut down, restart
Start "GO Launcher EX"
Go to "Play Store"
Search for "Kindle Android"
One of the option tabs should be to uninstall
Your books should now be back.