Ok, the fault is on the duet side maybe. I have the same problem now with a heater that have in use 1 year. I see an unnespected raise of 15 degres before the fault. I think that causes the burned spots in the thin point of the e3d cartridges. After the failure the duet becomes too lazy to respond if not reset first, 5 seconds or more to take a gcode command. Cant use the M562 command or reheat the hotend, and the m122 command never be read. Time to erase and reflash to try again