Cannot open files from iCloud drive on Mac but they open on iOS devices
Had this issue - 
Opened System Preferences - iCloud - UNselect iCloud Drive (confirm removing local files) - reboot.
Login again - do the reverse:  System Pref - iCloud - Select iCloud Drive.
Have a touch of patiences when you try to open files as that takes a few minutes to get everything back in order.
Worked perfectly for me.