Scroll to disable Control Flow Guard (CFG).
You might improve the performance other aspects of Visual Assist in Visual Studio, at least with respect to the effects of tighter security in the FCU, by disabling all 21 program security settings specific to the application.
Apply, and restart your PC.
You can improve performance of all affected applications in the FCU by disabling CFG at the system level:
App & browser control | Exploit protection settings | System Settings
Obviously, disabling a security feature has its own cost, i.e. less security. You can learn more about the slowness of the API at TenForums and in the Visual Studio Developer Community.
Visual Assist build 2248 and newer do not suffer from the slowness caused by the Win32 GetPixel API. Update to the latest build of Visual Assist if you run Windows 10 Version 1709.