iBooks/Books Sporadically Not Syncing - We Know Apple SUCKS at Syncing, Though

[HUGE AL]

Mac Pro 5,1 running 10.14.6 (18G95). All backups and as much as can be done via iTunes (12.9.5.5) is done through there direct connected. Book Library will sync correctly about 20% of the time. Other times, only about 30% of the books appear on the iPhone (X running iOS 12.4). Have toggled the "All Books" and "Selected Books" a few times with varying degrees of success, but still random.

Any fixes, greatly appreciated.