A bad PNP switch (gear position sensor, located right on the trans itself) can cause many seemingly random behaviors in the trans including ones that seem to be related to temperature or other variables. The PNP has several contact tracks in it. They can wear unevenly causing different ones to miss at different times. Sometimes the trans will recover for a while.

I had all the problems you describe with my 95-850 and they all went away when I replaced the switch.

If the PNP was replaced before maybe it has gone bad again, is dirty, or was not aligned properly. A PNP might last 5-6 years. Gear position sensor problems occur in Fords and other cars, not just Volvos.

I would probably consider whether the car seems to have had very hard use overall, like badly worn seats, loose ball joints, etc. Many trans failures on various car makes can be traced to abuse. The mode selector or other interior switches would not usually fail unless something was spilled inside.

Good luck...