How to unsync books between devices

I was trying to sync a book from my iPad to my iPhone. I decided to click syncing iCloud Drive on both devices. Now both my devices have all my books. I like to keep certain books on my iPad and certain books on my phone. When I unclick iCloud Drive ALL the books on my iPhone get deleted. Even the ones I have downloaded. Same thing happens on my iPad. How can I go back to normal without having to manually redownload every book on their individual device? When I stop syncing books on iCloud it removes all the books too. I just wait to keep them separate like I used to have it