Overlay not working over "settings" (Galaxy S9 / Android 10)

Hi all,
I have a problem with overlay over a unity VR app. After some analyzing, I found that overlay also does not work over “settings”.

Here is more detail:
I have Galaxy S9+, running on Android 10.
I wrote an app, displaying an overlay over any other app. This works over most apps, but for some apps, when you give them focus, the overlay simply disappears. And reappears when you put a different app in focus.

Following insights so far:

  • on different Android 10 phones, this works
  • on Galaxy S7, this works
  • even on Galaxy S10 (but running on Android 9), it also works

So what is it that’s different with Samsung’s Android 10 on Galaxy S9?
I am quite sure that the apps where the overlay does not work, just display themselves on top of the overlay, instead of the other way round.
I am new at getting into Android-device-specifics; any hints to documentation of Samsung’s specifics as a starting point to further own research would be highly appreciated.
Thanks!