Do you have RSE (Rear Seat Entertainment)? On mine in order to watch the DVD on the front screen you must press the audio select button twice. I have found if the last time I drove the car the RSE was used I must press the audio button twice to restore my screen functions. By chance I would give this a try even if you do not have RSE. Maybe there is an electonic switch built into the display in the event the vehicle is optioned as RSE.
Me: 3 Tribecas (2008, 2011, 2014) 2017 3.6R Outback Touring Currently
Wife: 2016 Crosstrek
10th Subaru Family