Old topic, I know, but wanted to add to it.
I never really paid attention to it before, just attributed it to tire slippage, or just how the system handles transitioning from the regen braking to the service brakes as speed decreases. However, I experience the exact same sensation in my 2014 FFH.
I have to make a right hand turn at the bottom of a hill every day to get home from work. The hill is long enough that I can coast and achieve 50MPH, though most of the time, I stick around 40 due to the turn (woo, free energy for the battery!). Usually, I achieve a 100% brake score on this hill as I have really timed it out on when I have to brake and how hard I have to break. By the time I enter the right turn lane, I am going around 30MPH, and when I make the turn I am usually somewhere between 5mph and 15mph (weather depending and the mood I am in). Quite often, I will feel the car lurch forward as if the brakes went out, then suddenly brakes will return just a fraction of a second later. Since I didn't actually come to a full stop, I don't get a brake score, but I know it would be quite high (easily above 90%).
There are no potholes, manholes, or anything else on this turn. We live in the middle of the country, so there are not even curbs, let alone manhole covers. Just nice, fresh, smooth asphalt. This happens basically any weather (I live in MN, so I get all the extremes), with any cargo weight, and basically any battery charge (except when it is full, in which case the service brakes are already engaged).
I get the feeling its something about how the car is trying to transition from the regen braking to the service brakes in the middle of the turn. I *sometimes*, though extremely rarely, get the same sensation when going down a long hill and the car suddenly transitions from regen to service brakes due to the battery being fully charged (around 70 on the SoC). I have never heard the ABS kick in (you can usually hear the ABS pump whining when it is actually being used), so I don't think its an ABS issue on its own, but something with the transition between regen and service brakes.
At this point, I just expect it to happen, so I always counter it by over braking during my turns. I have been driving the car for 3 years now, and of all the quirks, this is definitely annoying, but something I have trained myself to expect and work around.