I know that hill coming out of Stow , must have been a real "brown trousers" moment .
I suspect it is somewhere in the electrical system, but tracking it down is going to take some detective work.
A few suggestions:
Is there something near the battery isolation switch which could be "nudging" it slightly?
Is the battery secure, or does it move in its cradle ?
I don't know the Aero wiring at all , but is there a relay in an ignition circuit that could be failing intermittently? Incredibly difficult to track down , some perhaps replace the relays with new ones?
I would also check the fuses controlling the ignition circuit , I think the SS is Canbus? This is outside of my knowledge.
If there is an OBD II port somewhere try plugging in a code reader and see if any fault codes come up.
