I do not think the problem is in Nokia, but Google. Although I personally do not have a problem with the running applications in the background where I have them in the list: Settings - Battery - Background Activity Manager - enable blacklist - Here I have a unmarked application that I want to run in the background. It has 12 apps and they run smoothly in the background. And I listen to music for 4 hours. But as I read on the forum I'm probably only :(
I've had the same problems on Android 8.0.0 on the new Nokia 7 Plus. My brother has also had the issue on his Nokia 8 - Android 8.1. The problems seems to be with the builtin PowerSaverG3 app: com.evenwell.powersaving.g3
Hopefully Nokia do something about this app
No, you are not alone.
I'm a developer of an app and i'm facing the same problem on my Nokia 7 plus. My app is killed after 30-40 minutes, even when it's whitlisted on the phone. Also some of our users reported the same behavior. Only on nokia phones.
Same problem on a Nokia 6.1 (TA-1043) with Android 8.1.0 (with May 2018 security patches).