Today the same thing happened to my UR22.
I plugged a condenser mike in and switched on the Phantom Power, which led to the UR22 disappearing from my MacBook Pro. I tried unplugging the USB and replugging it. My Mac recognizes the UR22, but there’s no sound except a pulsing thumping sound and a blinking light on the unit.
Same thing no matter what (Phantom/no Phantom, mike/line plugged in, headphones, line out etc). Anybody knows what’s going on with these units?