Basically what happened was an upgrade that got an error, followed by an upgrade that never rebooted (first down to v26 and second to v32). I waited a while on the v32 reboot and then turned off the car. After that it would just blink the power light and spin the disc, but not read anything

I have tried disconnecting the unit for extened periods of time with no effect. I think the unit is stuck - I know it is hard to kill MK4s, but I think I must have timed it right to do so.