Mine is at the stealer at this time for the same fault, also my IDrive
display takes up to 15 sec. to come on sometimes.
Had a call today, and it seems that they could be connected
.
There is a lead between the battery and the computer with a sensor, and this
lead is telling the computer that the battery is only 30% (it's not, it is actually
85%), so with this the computer shuts off the heated rear window, and
the screen to save power, when the engine is running it tells the screen
to come on, but it tells the heated screen to go off as there isn't enough
power??.
Will tell you what happens tomorrow when the new lead is fitted.