Follow up – 24.5 hours after the first instance above, zone 21 malfunctioned again. With the door closed, it showed on and off multiple times until I bypassed the zone. This time the issues were limited to that one zone. I am not sure if I have a bigger issue or an issue with zone sensor. As I am not frequently at the home, I will swap out the zone sensor for another. Hopefully it helps. But still no explanation of why so many zones went haywire yesterday simultaneously.