App won't run in background

[Stretto]

If the app is not on screen, it will not download the files. e.g., if an another app becomes active or the screen goes off(but not to sleep). I do not believe this is a "background" processing issue in settings because everything is set to allow background processing. If one is trying to download large files it usually quite annoying because one has to monitor the device to make sure it doesn't go to sleep... also, one cannot use it because other apps will cause the client to stop downloading. This is for android 6