If things don't unzip at first, I'll give it a try on another computer or two with different OS and browsers as well to make sure there's no problem on my end.
If that doesn't work, I'd also recommend they resend using another service and send in smaller zips. wetransfer seems to be universally pretty stable,
and easy to use for clients around the globe, if there's an issue with another service. Wave files seem to up and download as quick as mp3s used to,
but there's still many places where the speeds and stability leave a lot to be desired. gl