I have encouted this couple of times now during 2000 miles of usage. Both times this what I experienced. Was driving at around 45MPH. Apply medium brake enough to stop in about 200ft from 45MPH, while applying brakes if a wheel go over a some bumps (of around 1 inch high) suddenly you will find the car moving without brakes, and brake padel dropping about 1 inch. You need to press hard on padel to gain control / brakes again. At one time I saw a message on dash which quickly disappeared. I think it read "NOT AVAILABLE". (I may be wrong it may have had additional words, I couldn't read this as I was in a panic and applying brakes). It is possible, that REGEN brake give up due to bad road condition and brake pedal dropped down.
I think you loose about 1 second without brakes before you gain brakes back, which could end up in an accident ? This is a safety concern for me. I took car to dealer, and they said everything is normal. It is not easy to reproduce this condition either.
Anyone else had similar experiance? Would like to know?