Hiya, I am confused. The point of Reality Converter is to convert other file types such as FBX into USDZ, so why are you trying to convert a file that is already USDZ, into USDZ?

I wasn't aware one of the aims was to open USDZ! Looks like you are correct. Never thought to use it a viewer. https://developer.apple.com/news/?id=01132020a

This could be an issue with exporting from Keyshot? Have you converted the USDZ from KEYSHOT into USD using reality converter?