Curious about a brake problem

This happened on a rental car not long ago and I am curious what caused it.

On Christmas Day we were on vacation on Maui. We had a very nice Chevy Impala. We drove up Haleakala, an altitude of over 10,000 feet. As we were coming down, I noticed a message on the dashboard. It said something like, “Brake assist disabled.” I’m not positive because it disappeared very quickly and I couldn’t get the message back.

After that there was a vibration from the front left whenever I applied the brakes. The brake pedal seemed to stick like it might not come back up after I pressed it, but it did.

The brake light never came on, and no other warning lights came on either.

I know what you’re thinking. You’re thinking I was riding the brakes all the way down from 10,000 feet, but no, I wasn’t. I downshifted the entire way down, and hardly used the brakes.

Traffic was very light that day as it was Christmas. I took the car back to the rental office at the airport, exchanged it for another car, and told them not to let it out again until they repaired the problem.

So, what was likely cause of the brake problem? It was not my car. I’m just curious.

Thank you for any answers.

Could be the abs brakes kicking in.They usually pulsate when pressing hard on the brake pedal.