The mod Electric Trains (1.4.1) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event ElectricTrains::on_player_mined_entity (ID 68)
ElectricTrains/control.lua:146: attempt to index field 'burnt_result' (a nil value)
stack traceback:
ElectricTrains/control.lua:146: in function <ElectricTrains/control.lua:144>

Error when mining the newer train of the mu-train combination (multiple unit train control mod).
You can mine the older one(s), but when you mine the newest train of the "mu-group", game breaks.

This probably isn't an MUTC interaction fault. Can you tell me if you were using batteries in the fuel slot?

Yes, there are batteries in all fuel slots

Found the issue, should be fixed now.