When running the app on an iPhone (tested on 5S) and there is currently an active connection to a personal hotspot (tethering), there is a "Personal Hotspot: 1 Active Connection" banner below the status bar.
When this bar is shown, the app doesn't launch as it hits an assert in:
[qtbase] src/plugins/platforms/ios/qioswindow.mm on line 210:
Q_ASSERT(m_qioswindow->geometry() == geometry);
Probably because the actual geometry of the viewport is smaller due to the banner shown