2018 Nissan Leaf forward collision avoidance problems

The incident occurred at a stop sign where I was waiting behind one other vehicle. The vehicle ahead of me accelerated from the stop sign to turn into traffic, but abruptly slammed on their brakes. I had began accelerating up to the stop sign and was unable to stop before impacting the car in front of me. As soon as I saw the vehicle was braking, I immediately slammed on the brake pedal. Braking did not immediately occur.

When the brakes are applied moderately at around 40MPH to slow down, and if a wheel go on top of some bumps or pot holes, car seems to loose braking power, brake padel drop about 1 inch, have to pedal hard to get the brakes back. At one time I saw a message on dashboard "not available" which I was not able to read and confirm, as this happened in a panic situation. This is occational but has happened to be 4 - 5 times now.