What does this "no live" icon mean in the iCloud photos web interface, and how can I fix it?

One of my photos in iCloud is showing an unusual icon at the top-left corner:

The normal icon for Live photos looks like this:

Non-live photos have no icon there. The photo is a live photo and it shows up as one on all my other devices. Only the web interface shows this odd icon. On the iPhone where I took the photo, the live photo plays normally. However in the Photos app on my Macs, it shows up with the normal Live icon but it doesn't play. Also there's a small icon in the bottom-right corner showing a cloud with an exclamation point. When I click that I get a dialog saying there's a problem downloading a full resolution version and I should try again later:

I have been trying again later for a week, so it seems unlikely to fix itself.

When I click the download button in the web interface, it downloads a perfectly cromulent HEIC image file, but no MOV. When I download a live photo I get a zip file containing one of each.

So it seems like something there's some kind of problem with the live-ness of the image that's affecting the live-ness of the photo. But what is it, and how can I fix it?

A quick fix would be to take the iPhone where it plays correctly and simply duplicate the image.

The new duplicate should then sync to iCloud and be playable on other devices.

When you are sure the new duplicate works on all devices, you can delete the old one.