First, there are 3 methods to add the camera to the app: P2P, IP/domain and local network. If the cameras appear as disconnected after disabling the Wi-Fi from the phone, you should check that the cameras have been added to the app by P2P and not by local Wi-Fi network.
If you have made sure that the cameras have been correctly added by P2P, then we'll have to verify to be using the correct app. You can find the link to the Android/iOS app store in the Download section of the product's webpage, or on the Nivian website: