Steps to reproduce: Starting a session. Mouse movement works fine in the menu, but as soon as the game starts, impossible to use the mouse.
Keyboard works, the character moves front, back and to the sides but no mouse movement.
Host or client: Both, solo and hosting with 2 other players as well as playing on an other hosts game.
Mouse: Logitech g402 and Razer Lachesis (both behaved in the same way)
GeForce GTX 760
Intel Core i3-4160 3,6GHz