I went in to diagnostic mode just to have a play around because I was curious.
After doing so, I found that I had lost my exhaust and intake temp display as well!
As mentioned above, the sensors need to be reactivated so for something such as exhaust temp you'll need to be in diagnostic mode and drive until the exhaust temp hits the minimum (400 degrees) before the sensor will be showing as active again.
Below is a picture of the screen after I went in to it and some functions weren't showing up as working.
You'll need to enter diagnostic mode with the engine on to try to reactivate these things.
This is a bit difficult to get the timing right because step 3 of the instructions is to go from OFF to ON while holding the joystick in.
To get in to diagnostic mode with the engine on, I had to time it right so that I pressed the joystick in during the time the car cranked over (and the power to the screen cuts out). Hope you understand what I mean..
So once the engine is on and you're in diagnostic mode still, you can start reactivating the greyed out sensors.
Eg. Speed, exhaust, F-torque, F/R and L/R G forces, brake..
And done!
Usually, a quick drive down the street will bring the exhaust temp high enough to get to 400 degrees.
I thought I could do it by sitting in my driveway holding the revs up but it was taking too long haha.
I hope this helps in some way!
Oh and also as mentioned, those sensors don't get disabled during compliance.
My guess is someone went in to diagnostics to play around and couldn't figure out how to reactivate it.