If the Control4 app can't connect to your system, first try closing the app and re-opening it. If that doesn't solve the issue, make sure you are on wifi, try adding a new system and entering your my.control4.com user name and password again.
Also, if you installed the control4 app on a new device, make sure it is the Red Control4 app icon and not the Grey one. The Control4 Grey icon app is for older system software up to 2.53 and does not work on new systems.
Current system software is 2.10, Red Control4 icon in app store or play store.