That's what you get for using Nokia. You're just stuck with those bugs. Nobody cares. Customer support doesn't exist.
Well.. I believe I sent more than that myself :D The problem with my bug is that HMD thinks they fixed it. But for me it's still going strong.
It's on the other device (Nokia 5). Apps close in the background as soon as other app is opened (like switching between 3 apps - there can only be open 2 apps, third one is closed, no matter how light on RAM they are). At one point a single app in the background couldn't even exist :D But they 'fixed' that.
The only fix I found is rolling back to Android 7.1.1 with which I'm staying now. But security is low now, no Oreo privileges/functionality and so on..