TL;DR. Fix by turning on User Account Control (UAC) and restarting the pc
I get the same when moving the mouse up or down, but also get my mouse cursor appearing on left or right monitor when moving the mouse to the sides. The cursor is hidden in the game until it hits the edges of the monitor and then travels outside of the game. Using a 3 monitor setup.
EDIT 1:
Disabling my other 2 monitors fixes the cursor going out of bounds to the sides, but up and down still reveal the top frame and Start taskbar.
EDIT 2:
Can now consistently reproduce the issue and fix it by turning on UAC.
--Open 'User Account Control settings' and move the slider and restart pc
--or change DWORD value of EnableLUA from 0 to 1 in regedit at Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System