I have also had this exact issue on my 2016 Nissan Leaf 30kw tekna. The problem has almost caused three accidents now and each time I take it to the dealership I simply get 'we cant fix the car if we cant replicate the problem'. Nissan Customer services have been as equally useless and keep telling me the same thing.
After reading extensively on this forum I understand that a 12v in bad health can cause boot up issues . I saw more issues with my car during lockdown as I was just driving to the supermarket 10 mins away once or twice a week. Is it possible that the car did not have enough time to charge up the 12v again during those short journeys and the parasitic drain zapped the 12v while the car was stationary? Is it worthwhile just turning the car on for half an hour per day to charge the 12v via DC-DC convertor or better to remove the battery and charge it in my flat. (i dont have a garage to use a trickle charger). Is it also true that making sure the climate control is on during journeys will boost the voltage going through the 12v and therefore charge it?
I have taken the car to an independent specialist and he has also found no faults with the car but he is changing the brake fluid - i'm a bit sceptical about this but its worth a try.
Has anyone had the intelligent braking control unit replaced in order to fix this issue? Apparently a new one costs £3000 so I would be incredibly reluctant to do this if I can avoid the situation and just keep an eye on the 12v.
This issue is causing me a ton of stress as my partner is expecting a baby in October and i'll obviously need a car when the time comes.
At the moment, its looking like I will have to sell up for a huge loss to a brokerage who buys faulty vehicles.
Any help would be hugely appreciated.