More than likely abs kicked it out sensing a slip indicated by wheel speed differential. Iv had this happen 2 times on bumpy roads
No lights are coming on, it just reacts like it would if you hit the brake. Hitting resume gets it going again.
I spoke with a buddy of mine this morning who is a very good mechanic. He suggested seeing if there is a way to adjust the switch that turns the brake lights on, making it travel a bit more to turn the brake lights on. He said it might be the brake pedal is bouncing a little on hard bumps deactivating it. It might be worth checking it out.