Make sure you haven't enabled the memory cleaner setting on an app/game, or in general. If you have this enabled on a game in Armory Crate, it aggressively closes all background apps when you access that particular game. There's also the function in the Mobile Manager: That also closes all background apps. There's also the Super Cleaner function, too. There are several features built into the phone for the sake of increasing performance and decreasing battery use, but sometimes they can be more aggressive than desired.
Hi! I have a solution to the issue. Do a long-press on the app you want to keep awake and press "(i) App Info" In there you need to go into "Battery" and turn off "Background app management. This will keep your app from turning off while doing something else, be mindful that the battery will deplete faster because of this.