Why service brake assist message keep appearing and sometimes when put gear in reverse break pedal hard to depress

I wish I knew...I have spent $400 and now have 3013 encore in shop and going to pay another $970 to try to get the same thing fixed....It happen sometimes when I back-up and also when I try to stop fast. Love my encore, but not that part! But when it happens, it is scary!

I am having this same issue on an AWD 2019 Encore - has anyone succesfully diagnosed this problem?

Me too. I have a 2016 Buick Encore I bought in 2018. Its Oct 2020 n when I tried to brake after I parked my car up front the brake felt like it was struggling n car felt like it was gonna take off. Then this Service Brake Assist popped up. Smh

I'm almost ready to sell this %#@ car!

So what is wrong? I have same issue, "service brake assist" pops up sometimes and after starting my vehicle brake pedal is hard for about 20 seconds, after that everything is normal.

I am having the same problem. I have a 2015 Buick Encore Premium. Took it for repair in March 2023 but still experiencing the same issue. Initially, the brake assist mesage randomly appeared, only affecting the Buick when in reverse. But now the brake pedal becomes like concrete when trying to slow down when driving. I just experienced that horror as I tried to park at a busy Academy store yesterday. In March, I notified my mechanic that there is a TSB related to this (#16-NA-36. He said it looked like the culprit was a faulty Vacuum check valve. He replaced the part at $186.25 and labor was $92.50, Total: $278.75. Everything seemed fine until a few months later, I was driving 6-8 hours to another city for a weekend concert. Hotel parking was on an incline and parking was tight. Now imagine my fear seeing the Brake Assist Message pop up multiple times out of nowhere while proceeding to back up in a downcline! I'm taking it back in tomorrow!