QuickTime movies disappear after uploading to iCloud Drive

I'm trying to upload QuickTime movies (.MOV extension) from folders on an HP PC to Icloud Drive. Two days ago it worked just fine, now it's not working. I tried uploading, and also tried dragging and dropping them over. It briefly looks like they are there, but then they disappear. I've tried switching browsers, tried re-starting the computer, I can't figure out why the same process I used one day, is not working 2 days later?