All zones set to something like 68. Randomly, not on every drive, the passenger zone starts blowing heat as if that zone were set to the max temp. Turning AC off and back on does not resolve. Usually, but not always. Parking it for a while (20 min) resolves the issue.

When under the 7/100 certified warranty, i took it into the dealer for this. They 'resolved' it with a software update. Once warranty ended, it came back.

Any idea what's causing this?

 

It might be the blend door actuator causing the problem. If it malfunctions or gets stuck, it can make the system blow hot air regardless of the temperature settings. This could explain why turning the AC off and on doesn't resolve the issue.
Also, check the temperature sensor and HVAC control module. Plus, I’d look at the wiring for the HVAC system.

 

Good tips. Thanks