You said you have 4 temperature zones in your house. Do you have 4 Nests or something else?
If you had a competent installer install everything, they would have made sure everything was hooked up correctly. But, even competent people can make mistakes. I have heard of systems when the furnace and heat pump were fighting each other. I don’t believe you have that.
The question is, how is your system set up to work. If the main AC (which is really a heat pump) is really only used for AC, is most likely does not need a pan heater (since it will never be used in below freezing weather). At 50W usage, you are looking at $50/year (if it is on all the time, depending on your electric rate). Since the heater is probably only on when it is really cold, the actual amount is probably much less. You can verify this by looking at you IotaWatt readings when it warms up some. This should also show if the heat pump is being used at all. If it really is just for AC, you can turn it off at the breaker during the winter. You will just need to remember to turn it back on in the summer.
It is also possible you have a more complex system. Since you have 4 zones, I say your system qualifies as, at least, unusual, if not complex. In a moderate climate, using the heat pump can be cost effective to provide heat. It depends on the cost of gas vs electric where you are. Typically, gas is cheaper (by quite a bit) per BTU than electricity is. The heat pump can still win, since it is generally more than 100% efficient. It can do this because it doesn’t generate heat, it just moves it from outside to inside. You generally need a very competent HVAC professional to set up a system like this. If you don’t already have one you trust, it might be worth finding one. Once you find one, they can advise you on what to do better than we can from such a distance. I say it is the pan heater and you probably don’t need it (and fixing this will quickly more than recover what you spent on the IotaWatt).