Reproducing this issue is pretty hard to do. I can't give instructions that reliably lead to the broken behavior. Nevertheless, I faced the issue several times so there really has to be a problem. Maybe you are lucky and can reproduce it with the following procedure:

1. Start Creator and connect an iOS device.
2. Create a new project.
   I used a Qt Widget Application project.
3. Run this project on the device.
   You might need to use a release configuration to make it even build.
4. While the application is running, stop it or disconnect it from Creator in one of the following ways:
   • Go to Application Output view and click the red "Stop" button.
   • Go to Application Output view, close the tab and click "Force quit".
   • Disconnect the device by pulling out the cable and reconnect the device.
   • Press the device's front button
   • Double-tap the device's front button and kill the app by swiping it to the top of the screen.
5. Repeat step 4 until the application can't be started anymore.
   Once this failed at my first try. In other cases I could repeat the procedure for ten or more times without any trouble.
6. Try starting any application directly on the device.
   Doesn't work.
7. Try double-tapping the device's front button to get to the list of running applications.
   Nothing will happen.
8. Turn off the device.
9. Try Turn to turn on the device.
   Nothing will happen.
10. To reanimate your device, keep the power button and the front button pressed until it reboots.

Stopping an application should not do any harm. Sorry that I can't nail the reproduction down more precisely.