I have P85+ I got just a couple months ago. It's on the latest firmware, so I've never had the low setting above a walking speed. This afternoon I set it for demonstration and then drove off. I'm on the freeway at about 40mph (rush hour traffic) and notice it's still in low. Did we get it back? Anyone else confirm?
Call the tech support. They can access your vehicle and change the settings from their end / see if anything is wrong. Also you could try to hold down the two rockers on the steering wheel for 10 seconds to allow the system to reboot, that may help.
I mean, I can set it to whatever setting I want and it will stay. If it's in low, I stay in low. If it's in normal, it stays there.