aif audio files on iCloud can't be copied or moved

I have quite a lot of aif audio files on iCloud. I've just discovered that many of them can no longer be copied or moved – at least not when accessing iCloud from my Mac; I can still download the files on icloud.com.

When I try to copy them, I get this message: "The operation can't be completed because an unexpected error occurred (error code 0)."

When I try to move them, I get this message: "The item "[file name].aif" can't be copied because there isn't enough free space." Though there's plenty of space where I'm trying to move them.

The aif files that are no longer accessible all have this icon:

While the aif files that I can still copy and move all have this icon:

Any ideas what could be causing this issue – and if it's possible to fix it?