On my 3.8.17 install, on E16 the (Fn)hardware brightness keys do not give any response.
The strange thing is that they do work if I switch to E24 Enlightenment ...... so this is apparently very E16 specific i.e not the system failing. 
Could it be that there is some sort of override there?
3.8.17 here too, using E16 as my workhorse, screen brightness keys work fine on a Dell XPS 13 (L322X).
They used to work fine on previous E16 installs and the funny thing is that they still work on E24 --- so I'm surprised that E16 reads key-events differently or not at all.
Off course I can also make E16 use specific keys but that's beside the point.
This shouldn't be happening in the first place.