2015 2.5L Chevy Malibu Problems Starting Car, Start/Stop, and Locked Radio

I had some weird errors with my Malibu. When I was driving in a parking lot someone suddenly back up so I hit the brake which initiated the Start/Stop I took my foot off the brake and the car stalled. Light came on saying service vehicle. I turned it off then started the car again no message and no problems...I thought. Then a few days later the car would not start when turning the key in the ignition. Only engine light came on takes 3-4 times then finally will start up. Mean while the Start/Stop has not been working at all. Then in one weekend my car would not start properly about 3/4 times. I took it to get the battery tested (New August 2018) Canadian Tire said it was fine so I took it into GM, they said there were two codes (didn't give me the codes) and they reset them but the start/stop wasn't working still and they weren't sure what had happened, then assured me that if it happens again please bring it back in. then not even a week later I got to start my car and it would not turn over again took 4 times of trying then flashed a message "Service Rear Axle". Then car turned on but the radio display was black, then the my link message appears then a message just says "LOCKED" on the radio screen. Then while driving the start/stop was working fine but a couple times when it would start up the message "service stablitrak" would pop up. The car is back at GM again today but I do not have any faith that they know what is going on. They have zero answers for me and thought I'd try on here and see if anyone has had a similar issue?? Thank you