If someone has already made the point I'm about to make, I apologize. I don't have the time to read every remark in this thread.
I don't think this is a bug. I think it's operating as Apple intended. In iOS development, there is a thing called "state restoration". State restoration in an app gives the illusion that an app was moved from the background to foreground when in reality it had quit and was relaunched. It's the responsibility of the app developer to implement state restoration in their app. They must write code to record where you are in the app and the data it's using. When the app is relaunched, the developer's code brings it back to the same point with the same data it had previously. Prior to iOS 13, when you switched from app A to app B and then back to A, it probably stayed in the background and wasn't terminated. That most likely isn't the case now. The problematic apps probably don't implement state restoration. The reason I think iOS's behavior is intentional is based on a remark made in one of Apple's development videos:
"In iOS 13, state restoration is no longer a nicety. It is crucial for your application to implement scene based restoration."
You can hear the discussion in the following link starting at the 7:40 time mark.
https://developer.apple.com/videos/play/wwdc2019/258/?time=463
My advice is to contact your app's developer and let them know you want them to implement state restoration. Really Apple should have let developers know in June 2018 that state restoration would be critical in the next year.
I don't think this is a bug. I think it's operating as Apple intended. In iOS development, there is a thing called "state restoration". State restoration in an app gives the illusion that an app was moved from the background to foreground when in reality it had quit and was relaunched. It's the responsibility of the app developer to implement state restoration in their app. They must write code to record where you are in the app and the data it's using. When the app is relaunched, the developer's code brings it back to the same point with the same data it had previously. Prior to iOS 13, when you switched from app A to app B and then back to A, it probably stayed in the background and wasn't terminated. That most likely isn't the case now. The problematic apps probably don't implement state restoration. The reason I think iOS's behavior is intentional is based on a remark made in one of Apple's development videos:
"In iOS 13, state restoration is no longer a nicety. It is crucial for your application to implement scene based restoration."
You can hear the discussion in the following link starting at the 7:40 time mark.
https://developer.apple.com/videos/play/wwdc2019/258/?time=463
My advice is to contact your app's developer and let them know you want them to implement state restoration. Really Apple should have let developers know in June 2018 that state restoration would be critical in the next year.