GE Model J S968S0F4SS. During bake display goes bake, oven turns off.

Oven will turn ON, but quit heating during the bake cycle. The display will go blank and heating will end. If the door is opened, the display completely lights up with all of the lights on. The clock is then displayed and the oven begins to act normally again. The oven has worked fine for baking, turned off during preheat, turned off after preheat. It's unpredictable. This is an expensive unit that's about 12 years old. I'm fairly handy and can diagnose and change parts, but this is so unpredictable it's hard to track down the cause.