Interface Removed From Computer Error

Hi there.
I was in the middle of something with Cubase 10.5, (there have been no issues at all with this iMac, Mojave, the latest tools for the MR816), when Cubase crashed. I restarted it, and a couple of minutes later received the message that the computer had removed my audio hardware.
I have never seen that error message before.
I have tried restarting Cubase, the iMac, checked the connections, reset the MR816, uninstalled the latest driver and tried rolling it back…all with no luck.
Any advice of what to try next please?
Thank you.