After many months of faithful operation this morning I flew home to this:
(pic taken after plugging and replugging the onewire SSR board in a panic)
I unplugged and re-plugged the cable to the Onewire SSR expansion board, there was no change, the fridge resumed cooling (freezing!)
I repowered the brewpi and the sensors all came back and sanity resumed
The Raspi was not interfered with
What did I do wrong? 60L of beer is ruined. Seriously pissed off right now.