I had this exact problem one year ago, took my car to the dealer (who had NO IDEA what this was, for $2,500!), yet changed both computer systems on my '10 Equinox. This problem has arisen once or twice shortly thereafter the "repair" and just presented itself more or less a year-to-date.
With no warning, upon starting cold or after a stop, the brake becomes HARD and won't release--therefore the vehicle won't move. When it does release ('if' it releases), the vehicle will stutter for a bit as if its not getting gas, then it disappears. 'If' this symtom locks in from a cold start or stop, the car will not move. You're stuck wherever you are! In the case moments ago, it didn't quite lock up when pulling away from a Stop sign.
ANY advice regarding this mystery fix would be greatly appreciated! I will add that when this originally happened one year ago, I got a Check Engine warning light on my dashboard, which has yet to to present itself again.