Hi, I'm sorry that you're having issues. Unfortunately, I have never run into this problem and nobody else has reported it so far either, so I'm not sure what could be going on. For starters, I would try running winsetup.exe and switching the graphics driver from Direct3D (the current selected default) to OpenGL, and see if that changes anything.
Also in the settings, you can click on "Advanced" in the lower right corner and see if increasing the "Mouse speed" slider helps.
It would also be interesting to know if this happens with other games or apps when they're running in fullscreen mode (like VLC, for example) to help discard the possibility that it might be some setting in your Windows configuration.
