M-Audio Xponent on DjayPro Mac - 1 controler works, 1 controler does not. Why?

I purchased Djay pro for Mac last spring to realize that it was not working with my 8 years old Xponent even though it says it does on the web page. Anyway, I got a refund and everything is OK.
After this, I got a recent Pioneer controler and bought Djay pro again. Everything is very OK.

Now… the weird part…
My son, to which I offered a brand new Xponent for Xmas 2-3 years ago, just before M-Audio stopped supporting the device. He was not aware of my experience with Xponent and Djay Pro so he bought it.

Surprise, IT WORKS!!! and he runs on El Capitan 10.11.6 !

2 questions:
-Why his works OK with Djay pro?
-Why mine is not?

Firmware version?