A/C and Heat not turning off when set temperature is reached.

I have a new issue where both my heat and A/C will continue to run after the temperature set on the thermostat is reached. It's a dual-zone system with two thermostats, both zones began experiencing this issue on the same day.

• Example: Set thermostat to 72 degrees, fan auto, Heat. The heat will turn on normally and will continue to heat until the room temperature reaches about 80 degrees. Tested multiple times and the heat will run until it reaches somewhere around (78-81 degrees).

• Example 2: Set thermostat to 70 degrees, fan auto, Cool. A/C will turn on and continue to run until the room temperature reaches about 61 degrees. Multiple tests and the A/C kicks off at different temperatures (63-59 degrees)

I've reset both thermostats to factory default settings and removed any schedules. I've also disabled WiFi on both thermostats.

I've had two different HVAC technicians (separate companies) take a look. Both almost immediately said both thermostats were faulty/bad and needed to be replaced. It seems unlikely to me that both thermostats would fail on the same day in the same manner. Quotes for new thermostats and installation is around $ quoted by both companies.

System Details:
2 x Honeywell Lyric T6 Pro Thermostats
Lennox ML14XC1

Let me know if there are other system details you need.

Is there some other component that could cause this behavior? Could two thermostats really fail on the same day and in the same manner?

source https://hvac-talk.com/vbb/showthread.php?2225882-A-C-and-Heat-not-turning-off-when-set-temperature-is-reached&goto=newpost