Sustained heavy load on the electric motor

The electric machine has been worked hard for long enough to reach a limit — towing, a long climb, repeated hard acceleration, or heavy traffic on a hot day.

This is the one cause in the electric-drive set that is often not a fault at all, and recognising it saves people money. An electric motor will deliver its peak torque more or less indefinitely as far as the driver can tell, because unlike an engine it does not run out of breath. What limits it is heat, and heat takes minutes to build. So the car feels effortless, then quietly stops feeling effortless, and the driver has no warning because nothing in the experience suggested a limit was approaching.

The signature is recovery. A genuine fault does not improve when the car is parked for twenty minutes; thermal derating does. So "it went flat on a long hill and was fine again afterwards" is the single most useful thing an owner can report, and it points here rather than at a failing part.

Where it stops being innocent is when the load is not the driver's doing. A dragging brake, a seizing wheel bearing, underinflated tyres or a binding driveline makes the motor work permanently harder than the road speed suggests — which produces exactly this and does damage while it is ignored. So the question worth asking is whether the load makes sense: if the car is derating on an ordinary journey rather than up a mountain with a caravan, something mechanical is resisting it.