Bosch Inverter Heat Pump Not working properly

Have a residential Bosch inverter unit, dual zoned, honeywell board, 2 ecobee thermostats. 3 times now, apparently when the outside temp dips fairly lower than normal for the S Atlanta, GA area, my heat simply shuts down during the night and we wake up with the interior temperature being in the 55-60 range. The unit outside is lifeless. Eventually when it warms up a bit later around 10 am, both zones begin to heat up as normal. Unfortunately the guy that installed mine, though an expert, was struck by a vehicle and killed in late August. Small company, good people, but none of his employees are near as skilled as he was. I'm not absolutely certain, but I'm assuming he installed a heat kit, cannot imagine he did not. Im still under a labor warranty. So the deceased owner's top man suggested 2 possibilities. 1. both ecobee thermostats went bad concurrently (lottery odds) almost certainly NOT. 2. I have a bad zone board, which they plan to replace this coming Friday. But if the zone board is faulty in some way WHY ON EARTH would the pattern be that this has happened 3 times and only when it gets especially cold outside? It was 25 degrees this am around 5 am when i woke to a very cold room. I called a HVAC company, that apparently does not service this area, and the owner was very nice. He spent some time on the phone with me. He questioned whether or not the zone board is wired correctly to signal the heat strips to come on when the normal heat pump cannot operate in such cold temperatures. That was my understanding anyway. My labor warranty is in place for another 90 days and I need to find a good company in my area (Newnan, GA area code 30263) to be available for routine maintenance and repair. Any suggestions on how to find a good one and know that they will know how to properly maintain, diagnose, and repair this type of system?
Equipment: Bosch 20.5 SEER IDS 2.0; Bosch Air Handler, Ecobee Smart Thermostat Pro Model EB-STATES5P-01, Honeywell zone board
Any comments or suggestions are very much appreciated.
CURT

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