I'm wondering what could be causing the 4-Wheel AHC System to fail on a 2009 LX 570. The vehicle is currently stuck in the low position.

"Check 4-Wheel AHC System" dialog on the dashboard and the ride height switch fails to do anything.

Has anyone heard of an LX 570 having these issues? What could it be?

 

First I have heard of it here. I did wake up to my LX470's rear end being way up in the air.

Your problem could be as simple as a sensor failure. Sounds like a trip to the dealer.