Hello there.
How did you make sure that the gpu running was your 940mx? From the behavior you describe everything points to the dedicated vga not activating (that would also explain the random game behavior you mention).
You can try forcing your gpu to activate with DoS2 from nvidia control panel or try to make a clean install of your drivers (completely uninstall everything hd graphics/nvidia related then reinstall the drivers of your hd graphics/nvidia preferably from your laptop's manufacturer site).
I hope it is something as simple as that cause your specs seem fine for this game (i run dos2 on 1080 on inferior lap than yours (i7 4500u and ati 8850m) with 30-40 fps most of the time).
