I've used the built-in Pandora app on two GM vehicles, one a 2017 Chevrolet Cruze, and now on my 2019 Chevrolet Volt. Each of these vehicles have done this sporadically. Typically at least once every two weeks or so. When it happens Pandora's built-in app does NOT recover no matter what you do until the vehicle sits off completely for at least 15 minutes. I've had this happen even at times the 4G LTE for the vehicle is showing full bars even at vehicle startup. The Cruze had this issue as far back as 2018. I've had this happen on my Volt as recently as just this week. I can also verify when it refuses to work, I do still have WIFI coverage for the vehicle as I can use the Pandora app on my cellphone and still use my car's hotspot with no issue. So this is either a Pandora app issue on GM vehicles, or some kind of integration with the data stream that flakes out regularly. About 95% of the time this happens, it won't work as soon as the car is started and never recovers. I have had about 5% though where it'll be working fine, then suddenly stop playing a song and move to the "waiting for coverage" never to recover. It's especially annoying when I'm already driving and sometimes on an hour+ drive and it just refuses to work so I have to dig my phone out of my pocket and launch the app and stream from my phone instead. I hope this can get fixed and this information is helpful! 
