This isn't a bug with 1SE but a well-known industry problem with iCloud Photos. We're trying our best to address it but it's a moving target. 

The best workarounds are to log out/log back into iCloud, download the video locally in your Photos app, or check your device for available storage. 

You can read more on the documented issue here: https://www.imobie.com/support/how-to-fix-error-downloading-photos-from-icloud-photo-library.htm
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Sorry this is happening!