Does i happen if your not using teamviewer or similar software in the VM?
It happens even to a desktop background. Also the icon which you see when you lock your desktop was "scrambled"
What NVIDIA Driver Version is installed in your environment.
vMotion Support came with NVIDIA Software Family 7.0 - which is a Driver Version >V410.
Maybe you need to upgrade your ESXi vib and Windows Driver to a new Version.
We have version 410.68-1OEM.618.104.22.16869922 installed on our esxi hosts.
Which is release 7.0.
we had the same issues in our environment and after upgrading the nvidia driver to 7.1 (410.91-OEM.622.214.171.12469922) the problem is solved.
We have the some Problem with NVIDIA driver 7.2 (410.107-412.31)