GLC 350e cooling issues

There’s a coolant temperature indicator for the gas engine but from what I can tell the fault light is for any of the three cooling systems (2 on the engine and one for the battery.)
When it runs properly the vehicle is an absolute road machine. One just has to be cautious about going somewhere on battery power, which defeats the purpose of have a plug-in car.

So far the dealer has replaced one of the motor/pump assemblies, a temperature sensor, the controller for the coolant at the battery, the engine wiring harness, upgraded the software for the engine computer, and repaired a connection on the wiring harness. The problem is still there.
As much as the wife loves the car, we’re at the point of turning it back in as a lemon. If the dealer, the corporate office, and the factory all working together can’t properly diagnose and repair a problem than I don’t want to be on the hook for figuring out what it is when the warranty runs out.