To verify you can use the demo app here:

https://github.com/FalsinSoft/QtAndroidTools

To reproduce the issue follow the following steps:

• Open the app
• Don't do any action and wait the device to automatically turn off the screen for inactivity (or press the power off button in the emulator)
• Wait some seconds
• Go back from standby by pressing power button

Once done (not all times) you can see the main app interface (where controls are painted) totally black or, in some devices, you can see like a screenshot of the device desktop below. To show again the app interface just touch some controls (like menu or button) to force app repaint.