According to Microsoft, the ‘mouse lag’ issues vary depending on the game or input methods used. Some of the issues noted include:
1. Mouse jitters (jumps forward and back) as you move it through a game - This occurs in some games because Windows 8.1 handles the games’ checks for the mouse status differently.
2. Mouse movement is not to scale even after acceleration is turned off - If you have turned off acceleration to make the distance on the screen match the distance you move the mouse, that may not work correctly anymore.
3. Measured mouse Polling Rate has a lower reporting frequency than expected - If you have a gaming mouse that has a high frequency, when you test it, you may find it is reporting a lower frequency than you expect.
A workaround for the aforementioned issues is to go to the game’s settings and enable raw mouse input. In the same post, Microsoft has also listed some easier workarounds for other issues, such as the mouse not reaching all areas of the game window, and the inability to left-click with an integrated pointing device immediately after pressing a key. The former requires you to disable DPI scaling; the latter can be solved by changing mouse delay to zero in PC Settings.
Source: Microsoft Community.