Syncing photos to iPad Air 3 from Photos app on Mac running MacOS Catalina

I had some problems similar to this a while ago. It seemed that my libraries were seriously out of sync. In my case, four libraries were involved - my Mac, my iPad, my iPhone and iCloud itself.

As it turned out, part of the problem was that my iPhone was set to keep all photos so it was continuously downloading the images from the cloud. This activity, in turn, seemed to bog down the whole sync process across my other devices. I’m wondering if this might be the case for your iPad. Once I corrected this, things settled down after a while and the images started syncing as expected.

So, my recommendation is to review your iCloud Photo settings on all devices to ensure they’re set to your preference. I’ve got my mobile devices - iPhone and iPad - set to optimize storage while my Mac is set to keep the full library since it has the space and along with the iCloud copy serves as part of a two copy set of all of my photos. If something goes wrong with my Mac, I’ve got iCloud; if iCloud goes offline, I’ve got my Mac.

I actually also have this all backed up to Time Machine and Crashplan as well, so lots of backups but what I do is probably overkill for most.

I have also encountered problems with broken images in Photos after older libraries were upgraded. Some were linked files outside of the library that had moved. I had no choice but to delete and re-import those as my attempts to match the files through Photos just wouldn’t work. No big deal, just delete and drag the folders back in.

But some were stored in the library and I had no idea why they lacked thumbnails. I also couldn’t open them in Photos or online in iCloud. Referencing the metadata, I found the files which I also had kept on one of my drives but I don’t know how they got corrupted. It was a small number of files and I ended up re-importing them as with the other issue. There are ways to look inside of a Photo Library directly by viewing the package contents of the library file but you don’t want to mess around in there to much as you could break things. I would use this as a last resort had I not had the files stored elsewhere that I could re-import.

Syncing Photos library to iOS devices via iTunes has be very flaky for a very long time. There is a huge thread about this:

https://discussions.apple.com/thread/250716707?page=1

p.s. I have unsuccessfully tried every tip and workflow to sync images. Initially it might seem to work but at some point numerous missing or duplicated images on the iPad Pro. At the moment I am doing another sync, this time I once again try to sync each and every album one-by-one which is laborious and time consuming. So far all albums have synced all images (previously when trying to sync all at one step there were thousands missing images and repeated syncs either did nothing or increased the missing image count). Now it is at "Waiting for items to copy" which might take a few minutes up to many hours, you never know. The reported "Copying photo n of n" image count sometimes matches the updated images but very often it is something very different and sometimes a minor update seems to affect the whole library with tens of thousands of images updated. IF I ever get current images to sync, I hesitate to do any updates because previously that has failed no matter how I had done that. I have heard that with iCloud the sync should be OK but I bought the iPad with max memory so I could store the images and movies there. At the moment that seems nearly impossible. /rant

Update: to my big surprise, this time when I synced each and every image and movie album one-by-one, all files were successfully finally synced to the iPad (I cleared all albums before starting and carefully left 50GB free space on the iPad because once I got in some trouble when the storage got full -- syncing a blank folder took care of that then). But time will tell how the updates will behave later -- maybe I delete the the album needing an update before syncing an updated version it although that is more time-consuming (but I have unsuccessfully tried also this numerous times).