The small quick release connector for the extruder heater recently failed. This was discovered half way through a print when the extruder stopped heating.
Initial thoughts were that there was a software bug due to the extruder failing to extrude filament after 12 hours of continuous operation. However, some fiddling with connections revealed that the plug and socket connection was the culprit.
Replacing the stock connector with something more robust is straightforward but the process is a little fiddly.