2018 Off Road DC brake issue. Any ideas?

I tried searching this forum first. My son has a 2018 Off Road DC with 10,000 miles on it. Under normal driving, when you come to a complete stop (normal braking pressure), the truck will stop fine for about 10 seconds and then slowly roll forward. You have to push harder and it'll stop again but start to roll forward again. Eventually the pedal goes to the floor. Took it to the dealership and they couldn't replicate after several "hard" stops. Not sure if by doing several hard stopping cycles the problem alleviated itself, but the problem went away for 1 day. It's doing the same thing now. Kind of disturbing to be slowly losing your brakes. I'd have to assume something is wrong with the master cylinder as there are no leaks anywhere. Any ideas?

 

Take it back to the dealership, and contact yota corp if the problem persists and the dealership doesn't help.

 

When it starts to do it bring it back to the dealership. Go for a ride with the tech and show him/her exactly what your doing to get to happen. Leave the truck at the dealership until they can replicate the problem and fix it. Call the Toyota customer number and explain what is happening and that your concerned with yours and others safety.