Tried usb 2 and an older one along with several brands of usb 2 all fail at the same point.
I gave up after around 6 goes at it.

My car is a 2010 with the cic but it won't update.
Plug the usb stick in and it starts updating but fails at 56%.
Tried many sticks but the same every time.

As above but look at the wires going to the injectors.
I had something very like this and it was one wire had rubbed on the steel injector pipe ever so slightly.

Where they new injectors as i had this same problem and needed 2 injectors.
Cam-sensor didn't see that in your list sometimes don't show a code.

I fitted LED's to my mains 5 years ago but nothing said at mot time.

Was thinking of re-gassing the new to us 320d but i would jinx this good weather lol.
Might just do it on Saturday morning as i get free use of the machine at my old m8's garage as long as i do it myself.

Mine is cold that cold i turn it off sometimes for a short time as i feel i need my coat on lol.

How long has it been using that amount.
The undertray will hold a lot before it drips.

Tyres.
You say fronts relatively new what tread is on the rears.

Excellent advice list there.

No codes no worries.
As said could just be a backlog of soot to clear out in the pipe.

Just looked ant is it the fault code scanning it does.

What does Bimmerlink do.
Got Bimmercode and just looked at Bimmerlink and it is £34.99 the same as code.

I paid £70 for both worth every penny even if you only use it occasionally if something goes wrong anytime you will always be able to scan and see what faults occurring on the spot mines plugged in constantly and regularly do a full scan to check or put dpf section on which shows all temps and dpf ...