Pulled the MID to look into why three of the buttons only worked when the unit was cold. After ~10mins of driving, the three centre buttons would stop working. Couldn't call up CDs 4-6, use timers or check distance or speed etc.
Couldn't see anything obvious but I removed and re-seated the button connector cable (wide grey ribbon cable with black connector) that runs from the front PCB to the main PCB. Put it all back together and 24 hours later it's still all working correctly, regardless of run time or temps.
$0 fix - what I call a win!
(still need to address a couple of missing columns of pixels but they don't actually make the display unreadable - yet. You can see the missing columns in this video -
https://youtu.be/hjuf_vDIWC4).