After the launchscreen, but before app is loaded, there\'s a \"Loading from pre-bundled file\" message that appears at the top of the screen for just a few hundred milliseconds.
To disable the developer menu and therefore your mentioned message, you should change your Build Configuration
to Release
.
For iOS open your project in Xcode and select Product → Scheme → Edit Scheme... (or press ⌘ + <). Next, select Run from the menu on the left and change the Build Configuration to Release.