You could try to run the console command in a blueprint that sets the viewport as full screen, so you don’t have to run any Engine functionality that could interfere with your code.
Tapping F11 may run Engine code that resets all controllers to just one port (as a part of the expansion sequence). Could be an oversight. Who knows how they programmed it.
Maybe put it on a timer. Up to you.
It reminds me of the situation where someone wanted to set the ESC key as a key to open their In-Game menu, but it would just exit out of the Play Mode instead.