Are you measuring voltage while it is attempting to power up, or open circuit voltage? As
I said earlier, you should try to hook the thermostat up as close to the furnace as possible to determine if it is a problem with the wiring or a problem with the thermostat. If the thermostat keeps resetting when hooked up to the furnace at the splice point, then you should contact wyze and get a replacement. If it works properly there, then the next step is finding all bad connections in the wiring- you may need a tech for this.
Just having sufficient voltage available when nothing is hooked up to it is not enough, it also needs enough current availability that the voltage won’t drop below the operational threshold as soon as a load is applied.