Probably a firmware fix... but when LiBCM has turned itself off - or use has turned off IMA switch - BATTSCI isn't sent fast enough, which causes MCM to throw a P-code.

Fix:
Required several firmware changes:
-CEL fuses set to 0b10, which boots 4 ms after PoReset
-bootloader bails immediately if keyON is high (i.e. key is on)
-firmware initializes display on keyOFF (because 4x20 display timing requirements suck).

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Solution:

It's not specifically required (because LiBCM can now boot fast enough (with the above changes)), but I'm going to add a DNP 100 nF + 20 Ohm from +12V_LiBCM to buck enable circuit.    This sends a pulse onto the enable line when the IMA switch first turns on.