I'll try to explain the best I can since English is not my first language.
I'm having this issue randomly, sometimes happens, sometimes don't but is something that happens 80% of the time. When I point something to something that is up like first item on I can see "Windows" cursor at the top of the screen, when that happens, even if I can look around and move normally, when I try to click (like shooting) it does nothing and after several clicks, I end up at clicking at my desktop; is like the cursor falls out of the game to interact with the desktop. So, whenever I point up like watching the sky or something similar, is like the cursor goes out of the game, I can still move around but the clicking part doesn't work (right click to zoom or left click to shoot) and the clicks interact with the desktop, producing an "alt+tab" action like, I can go back to the game but it's annoying since sometimes I'm in the middle of a fight and I can't shot.
Any idea how to fix this?
Thanks!

First guess: you're set up to play the game in "windowed mode." This means the game is in a "window" (like a browser "window") and thus cursor can fall outside of the box and do desktop thingies.

When you launch the launcher, under Options, make sure the Windowed checkbox under 'Mode' is not checked.