Ok, I have done some more testing on this issue. This is what I discovered:
1) I can trigger full resolution every time only after I do the following steps:
a) Turn off "Power Mode" This is not battery power mode but Samsung performance mode option;
b) Change resolution to 1080p;
c) Start my game;
d) Exit my game and also do a force stop (from Settings->Apps->My Game). Because if you close it from task manager it still runs in the backround. I don't know why this happens.
e) Change resolution to QWHD+ (1440x3040);
f) Run my game again but only when phone is in portrait orientation. And only at this point application is started with highest 1440x3040 resolution.
2) This process above works only once and after that every time I start application it is always opened in lower 1080p resolution. If I want to get highest resolution again I need to change resolution back to 1080p again, start app again, close app again, change resolution to 1440p and then finally start app again only from portrait orientation to get full screen resolution.
3) There is also one more thing. When I go to the Settings->Display->Full Screen Apps->My Game and set it to full screen the message is displayed 'This app may not work properly in full screen'. What is strange about it is that this message is only shown for my game. When I change full screen settings for other apps this message is not shown. Can this be the problem? Is there any settings in AIR that should 'convince' Android or Samsung that app is optimized to work in full screen mode and with highest resolution?
4) But there is also issue where application is opened with different resolution if you opened it from landscape mode and when you opened it from portrait mode. If you opened it from portrait mode it will give you a little lower resolution (1080x2280), but if you opened it from landscape mode it will open app with a resolution of (1121x2367). And this is all working like this while the resolution of the device is set to 1440x3040.
Can you guys test on your phone if you are able to change resolution when you set that app should run in full screen mode do you get the message that says that app may not work properly in full screen?