Arma 3 external monitor troubles

Hi,

recently i bough new 24 inch monitor to play some games on it with my laptop. When I try to run Arma on that external screen, my FHD resolution looks like as if it has some serious underscaling and picture is shaking. If I duplicate both my screens , its bugged on external screen, but looks normal on laptop LCD. I tried some other games and all of them work fine with external screen.

More over other resolutions than FHD dont have this issue in Arma. When i try Borderless window or something like that, picture is sharp and it cuts my FPS in half, no less.

Im not sure if its relevant but these are the laptop specs

Acer V15 nitro black editon (15,6 inch ips)

i7 4710 hq

gtx 860m

16 gb of ram

Please, do you know of something that might help? :)