iPhone Issue

For a few months now when I am on my phone all of a sudden the app I am on will minimize and my phone will be on the home screen. The app isn't crashing once I click back on the app it is still open and in the same place as before it minimized. I have done everything that you will want to tell me to do. I have hard restarted my phone. I have deleted the app (although it is not just one app) and reinstalled it. I have made sure all updates on iOS and all apps are installed. I have even completely erased all settings and data (reset to factory) and reinstalled everything from the cloud. The problem persists!