I had this issue on two bikes and posted a YouTube video about this for the factory.
Sorry to say its not a firmware issue, but reading between the lines its a controller fault, though you will not get the factory to admit it.
Luna cycles in the USA says somewhere in their latest BBSHD product description that the BBSHDs they are selling do not suffer from the throttle /pedaling cut out fault, so Luna's buying power got the Bafang factory to fix it.
I tried getting a fix from the seller in China and they gave me all sorts of BS, even saying it was to protect the motor, which as you can imagine is exactly the opposite.
I can say, unless the Banfag factory are stupid, the Firmware of the good and bad controllers is identical, I have checked both and also copied working parameters to the faulty controller to see if that fixes it, it does not.
The way I sorted it was to permanently disable the PAS function by removing the magnets from internal crank sensor pick-up, a sledge hammer fix, but I absolutely must have a throttle as it fundamental to how I ride.
The only real fix I know of is to change the controller for a good / known working one and that's the challenge - how do you know other than to test it, because you cannot tell by checking the firmware revision, as it was the same on all my units - that is both settings & Firmware revision is the same.