My game quit from chat, hero menu, invasion, heist and more areas when i click ‘back’ on my phone without confirmation msg…
I reinstalled the game but that didn’t fix it!!!
I’m not exactly sure what you’re describing, but it sounds like normal behaviour? 
The game exits without confirmation msg… what is normal in this dude?
I think what you meant are unexpected game crashes. One of the causes of sudden crashes could be the amount of GB the game has and how your phone can handle it, or other causes some players may have mentioned about the crashing. But in other words, the GB(depending on the amount of cause is perhaps one of the causes of the game crashing.
I don’t think it gives out a message saying something similar to, “Your game has crashed, due to an unexpected inconvenience. Please restart the app.”.
Ah I see, it sounded like the game was just exiting from the areas described, and not closing the entire app.
Hitting back should only push the game to the background, not close it… like @SoulStorm said, it could be crashing
My phone handles it perfectly… it happened after last update
I have Galaxy Note 9