Joystick problem - BRAND NEW Mavic Air

I’ve just received my new Mavic Air and am having a problem with the fwd/rev channel not working at all.
To try and check whether it’s the RC unit I changed from mode 2 to mode 1 but the error stayed with the fwd/rev channel (ie. the problem changed from the right joystick to the left joystick) thus eliminating a faulty pot on the RC controller. The other channels (alt, yaw, slip) all work as should - just the fwd/rev does nothing!
I’ve noticed that when I hold the joystick fully forward/aft that the green status light at the rear starts flashing rapidly (green) until I release the stick - at which time it resumes flashing slowly… The lights at the front are red at all times (?)
I’ve checked/reloaded the firmware for both the aircraft and the RC but the problem remains…
Is there anthing else I need to check out or will I have to return the package as DOA?
After having waited impatiently for 4 weeks for the unit to arrive (due to Covid-19) it’s very frustrating not being able to try out my new toy!!
Simon