Cabin inside/outside air switch
 

So after some major service my switch has a mind of its own? It sometimes stays where I put it even overnight. Often after a engine off and then restart it resets itself to inside air only. What is going on?

Do you have the ventilation set to auto? On hot days the vents go to re-circulation mode to aid in cooling.

In recent years, the climate control systems of all Lexus (and Toyota) vehicles have been set up to default to the recirculate mode whenever the outside temperature is above (around) 75 degrees F and the system is set to auto or has the AC turned on. And, each time the engine is shut off and restarted, the system will revert to that default recirculate mode when the temperature is above 75.

Using recirculate mode will result in marginally improved fuel economy in some circumstances, but, when the car is started after it has been sitting in he sun on very hot days, the recirculate mode will actually cause the AC compressor to have to work harder to cool the cabin, and that will actually cause poorer fuel economy.

It opens and closes automatically. That can be changed in personalization settings.
normally if you want to heat the cabin the recirculation goes on until it reaches the set temperature. It is the same when you want to cool the cabin.