iTunes photo sync won't complete
so this has been going on for almost a year now, mostly on my iPad air2 and on my iPhone 7.... I sync pictures manually from my Mac to the iPad w/ iTunes . Sometimes i get sync won't start, cannot sync - internal device error, the photo app on the iPad crashes during sync or sometimes the sync just stops. All the while i see "syncing" in the photo app even after the crashes, rebooting and no connection to the computer. I have submitted numerous logs, reports, etc w/ senior advisors, updated to el captain, then sierra, to the latest iTunes 12.7.4 after downgrading to 12.6.4 and it still won't sync my photos. Any ideas from anyone? Id like to be able to manually sync my pics. Tks!!
PS there have also been times in the past when i have connected the device to back it up, and iTunes would sync pictures or at least show pictures were syncing even though i had not added or changed any since the previous sync session..... tks again
iMac (21.5-inch Mid 2011), macOS Sierra (10.12.6)