Are you manually closing the app in the background? I'm not sure how you're distinguishing an app that's open vs. closed in the background. Typically, you shouldn't have to worry, since the system will figure out when to completely close an app out of RAM. However, some devices (especially Chinese brands like Blackview) have firmware that is overly aggressive when it comes to killing apps in the background (to save battery). That may be the issue for you, and this typically can't be modified since it's baked into the firmware.