I was going to log an issue, but, I have since fixed it. I still thought it was worthwhile logging it as it may help out somebody else.
I was trying to assign a couple of buttons from my button box to Rob Romains Universal Dash. When I went into the "Controls and Events" or Rob's "Settings" plugin and tried to add a new mapping, the button press on either my wheel or button box did not get detected.
The fix was pretty simple in the end, albeit frustrating to find. I was pressing and releasing the button too slowly. I found I had to jab it quickly instead of pressing and release. Even a short press of, I guess about, < 1 sec was too fast. It needed a quick jab.
FYI, the button box is homemade so I know how it behaves. If I press a button quickly I get one press and one release. If I hold it down for > 1 sec I get two presses and two releases. I have no idea how the fanatec wheel buttons behave, perhaps it is similar. However, none of that may be relevant as I am fairly confident both the 'flick' and the 'press' were both < 1 sec in which case they should have been seen as the same.
However, in summary. If your buttons are not being detected, press and release as fast as you can, that should do the trick.