I have been successfully using LR Mobile to quickly crop about 1,600 Canon RAW images. Part way through this effort, the cropped images start showing up as black screens. I can three finger tap and get the correctly cropped image to show up, but if I move to a different picture and come back to the cropped picture, the black screen is back.
The images show up correctly cropped in the thumbnails.
Syncing is working fine to my desktop and the image is correctly cropped on my desktop as well.
Other smaller collections do not experience this behavior.