2017 Chevy Volt No heat when engine hot, but operting on battery

What is your question?

2017 Chevy Volt 1.5L plug-in Hybrid. By default it runs on the high voltage battery (HVB) if charged, but may turn on the engine due to the cold. I can put the car in "Hold" mode to force it to run on the engine, and not use the HVB, but when there isn't much demand on the system, like when stopped at a light or parked, the engine will turn off and run on the battery. Most of the time the car makes heat. BUT, when the engine coolant is hot, but the engine has turned off it doesn’t make heat. This can be because I switched from "hold" to "normal" mode; because I'm on "hold" mode but stopped at a stop light. It can be because I warmed up the car in the driveway before I got into it, and the car ran the engine because it was so cold but is running on battery by default. From all the other times that the heat does work, I can tell that the auxiliary pump, electric heater and heater core work. Had the for 3 months, I don’t use remote start and there are no dash lights or DTC’s.

What makes this problem better or worse?

Nothing I have noticed

How long has your 2017 Chevrolet Volt had this problem?

More than a month