It is interesting to note that although I fly the NGX a lot, I just landed a B736 BBJ at KCRW Yeager on a short runway and immediately noticed the autobrake yellow disarmed light above the switch.  Doesn't happen very often but there is no doubt that maybe I tapped the brake as I was working the rudder on a fun landing.  Yeager (Charleston WVA) was built by scrapping the top off of three hills and the approach to either end is over a valley with a steep increase in terrain up to the touchdown elevation.  This is one of more more interesting ones, and I've flown into it real world and it is equally interesting in person, which lacks the flat runways of the simulation world and instead provides a thrill ride just riding the runway.  My null zone for rudder should be 5% but maybe it got changed.  I'll check that next session.

I too have noticed this, that while touching down, the autobrakes don't engage and you end up sort of floating down the runway at 130 knots. I don't have any fancy rudder pedals, just the Logitech 3d pro with a high rudder null zone. I can't think of any reason my controls are conflicting and causing the problem. I use FSUIPC, but not for any controls, only autosave is being used. I've seen this issue happen to others as well. I wonder if it has to do with mesh or something as I remember that sometimes while landing at KSFO or similar airports, PMDG aircraft just slam into the ground without warning upon crossing the threshold unless you have the mesh settings set right in P3D. 

I, too, asked myself a lot of times in P4 now, "were the autobrakes working or were they not?" Once in ULLI they were not, but I blamed the add-on for it. Perhaps I was wrong.