Android 11 - Problem with landscape mode when leaving/returning to the app

Our App built with Flex 4.1.6.1 and AIRSDK 33.1.1.345 is landscape mode only.

When the user leaves the app to e.g. take a call and returns to the app, half of the screen will be black. It looks like the app is still cut of at portrait mode display width.

Is this as a bug with Android 11 or might we do anything wrong in the app?