The state of the template sensor sensor.front_door_battery depends on receiving a value from zwave.schlage_be469_touchscreen_deadbolt_2. When you restart Home Assistant, it may take some time before it sets up the zwave component and receives data from the schlage deadbolt. During this setup time, it has no value available to supply to the template sensor.
I believe that may be the cause of the error message Value cannot be processed as a number.