A similar thing happened to my crumble on my iMac, when it had been perfect for weeks. I did a whole bunch of basics before it got connected again. Took power off of crumble including through USB. Restarted the iMac, used a second crumble, same error. Tried a different USB lead, no joy. Restarted the iMac, made a cuppa, tried again. Then it worked!
My crumble was with the robotic vehicle it had always been with. The only difference was that I’d left the battery power ‘on’ for ages and it had drained them. Replacement batteries might have been part of the fix.