Books not syncing between MacBook Pro and IPhone/ipad

Since the upgrade to Catalina on my MacBook Pro, I noticed my ePub books, while still in “books” app on MacBook, don’t sync to my other devices. They don’t even show up in the “books” tab when my device is plugged in to my computer.

the only way I can get books to my iPad or phone is to airdrop them all (over 3000 books though).

There is a problem with this though.... if I then back up my device, it removes all my previously air dropped books.

Has anyone else got issues with iBooks not working properly?