As I suspected, the unit was low on refrigerant. Apparently the firmware in the PCB satisfies the fresh food temperature and then tries to satisfy the freezer. It doesn’t seem to read the fresh food temperature during that time. If the freezer can’t actually reach temperature, the system eventually times out (not sure if it’s freezer evaporator defrost or freezer defrost?) and tends to the fridge again. Service tap was less than -10psi initially. Adding some R134a refrigerant to bring up the pressure to between 0psi and +2psi (depending on how cold things were) made things happy again.