Go into you settings -> apps -> and scroll till you find the app MyChevrolet or myGMC
Make sure notification are allowed and location services are on and enabled. This app acts up if the location service is on.
Data Usage allow Background data usage.
Storage you can clear Cache. If you clear the Data you will have to login and set things up they way you want again.
App version I have is 3.16.1 (2677)
Now to be forceful about it.
You can also do a force stop and uninstall from here I would cycle the Phone before a reinstall as you are having issues with this app.
Also note that you can go into Setting -> Notifications -> MyChevrolet Even if it's enabled click on it and ensure it's enabled On , App Icon Badges on, MyChevrolet has a sound set
Hope this helps it sound more like setting issue or a bad or corrupt install.