On a trip several months ago, I was successfully able to copy over 300 RAW files to my iPad pro using Apple's SD card reader. I used LR mobile to edit and rate the photos, and they all synched themselves up to the cloud, and then down to my deskop PC.
I tried it again on a trip last week. Only a few of the RAW files synched themselves to Adobe's cloud when I was in the low bandwidth hotel, but after about a day back at home, all 375 RAW files synched themselves from my iPad to the cloud--and there they sit. I logged into my Adobe account today and confirmed that the photos are there, but none of them are on my PC.
The status message in the upper left of my desktop LR (latest version) has said 'Synching 376 photos' since last Saturday. Sometimes, it changes to 375. Not a single one of the RAW photos from last week's trip has downloaded itself to my PC. None of those images are in 'All synched photos'. I've turned synch on and off, I've rebooted, nothing seems to help.
Synchronizing the other direction, from the desktop to the cloud and back down to the iPad (which doesn't use the larger RAW files) works just fine. Using my desktop PC to add a photo to a synched collection, it immediately appeared on my iPad.
Pending synch activity under LR Mobile on the Preferences, shows "3 Uploading, 0 Downloading", which seems inconsistent with 376 (1 of the uploads is missing, 2 have errors--its been that way for months..it isn't worth the bother to do something about it).
Could you send me a LR Desktop diagnostic log, please? - best as a private message with a downloadable dropbox link.
You can trigger the log via LR Desktop preferences -> Lightroom Mobile and when you hold down the alt key you will notice a generate diagnostic log button
Its disappointing, but after trying multiple suggestions from Adobe, after 3 weeks, I'm still struggling to sync. The changes go up, but they don't come down.