iPad loses books when syncing
I'm an avid reader, but prefer paper over digital. I do keep a couple of books (8 in total on my iPad) just in case I run out of reading material while sitting in a waiting room.
Strange enough, each time I sync my iPad through iTunes on the Mac, I lose four of those books. At that time they don't even appear in the list of books that can be seen in iTunes. I boot Books, and there I can still see the books I want on my iMac. Usually, I have to quit iTunes, reboot it, and hope the books are now visible in the list of available books, so that I can select them again (if they were not selected; but mostly they are selected and will load when syncing again.
Just for that reason I will usually keep my iPad away from my Mac to charge it, as I know I will lose those books again, and will have to go through all the trouble to get them back.
Is this a well-known problem? Can anything be done?
Mac is running 10.14.6 and iTunes 12.9.5.5. iPad5 is running iOS 13.3.1, and this issue has already been going on for some time.
iPad, iOS 13

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