Official comment
This is a known issue.
Yes, we read these forums, and fixes are not made available in mere days, your patience is appreciated.
Before rekordbox 4.0.8 you didn't have HID support, so these functions are a step forward, and yes, one of them doesn't work when you push the button (but it DOES work if you click the CFX on screen in the software), so as a professional DJ, I'm sure you can appreciate that there is a work-around for it.