On iPhone, I don’t swipe up to close the ReSound Smart 3D app, generally. I keep it running all the time with Location enabled and set to Always On so that its Find My Hearing Aids feature has the best chance to work, should I lose an aid. The Smart 3D app does, of course, close if the phone has to reboot as after an iOS update or dead battery shutdown. I don’t turn my phone off at night either; I leave it on and connected to a charging cable.
Anyway, it doesn’t matter if the screen goes black with the app running; the app is still doing everything it should do when the screen is dark, as long as the phone is on. I wouldn’t leave the screen on all the time; let the screen go dark when the phone is not being used, unless your smartphone battery is way better than mine, or your phone will need a recharge much faster than if you let it go dark after a few minutes of non-use.
Dolores can you tell us why you think your Smart 3D app is shutting down? Does the sound in the aids change? Do you have an Apple or Android smartphone?