videos won't upload from PC to iCloud

It turns out that I *can* upload brand new videos, just not this particular group of videos. To review, the videos that won't upload were once in my iCloud Photos, but then deleted, and now I'm trying to upload them again. They were originally taken with an iPhone.

It's almost like iCloud "recognizes" these videos and won't upload them because it thinks they're already synced. In other words, since they were once already in iCloud Photos, perhaps whatever method Apple uses to distinguish what is "new" from what is already synced is getting confused? I've tried renaming the files (not transcoding, just renaming - they're still .mov) and changing the file modification date by 1 minute, but they still don't upload.

Does anyone know how Apple distinguishes one video file from another? Maybe some other metadata value that I can change and "trick" iCloud Photos into recognizing these as new?

Another screenshot showing what happens when I sign to iCloud and put a video in the Uploads folder. It says "Uploading 1 item" for a while, then "Updated 1 Minute Ago", but I still don't see the video in my collection.

Does anyone from Apple monitor these groups or am I destined to keep conversing with myself?

Just saw something new. Well, probably not new but I happened to be looking at the right time. When I tried (again) to upload a video there was a message from iCloud for Windows that said something like "File is not in a supported format". These are all videos originally taken on an iPhone and Windows reports them as Quicktime files. Furthermore, they haven't been edited. The filename and file modification date may have been changed, but nothing else.

No ideas? I don't get the error in the screenshot if I turn off Photo Stream, so could be a red herring. In any case, I still can't upload my videos.