Ed, just a note. This seems to be a generic error. My issue was that the folder did not have proper permissions where the USDZ file lived in the cloud. One i changed the permissions the error went away. For some of my larger models the error I get is Universal Scene Description Package Zero KB. This also seems like generic error. I would recommend downloading one of the Apple USDZ examples and trying it in your app.
https://developer.apple.com/augmented-reality/quick-look/
chrissPCS
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I also have the same issue here. Please let me know if you find a resolution.