Repeatedly getting unable to upload...try again later when attempting to upload a video file to iCloud.

I have been able to upload 3 files but only after exercising a lot of patience. Each one of the files failed to upload several times before finally uploading. The files are about 9MB each. They are MP4 versions of old video tapes. I am on my 4th attempt on a video. They appear to upload about 80-90% then fail with this message. I recently signed up for more iCloud storage, so there is plenty of space on my drive.

I can see by searching this topic that a lot of people experience this issue. But i have not found a solution that has made a difference.