virtualbox.org

I found that installing Guest additions on Windows 10 in VB 6.0 cause the display to "Lock". You could use the system, but the display would not update. Toggling Full Screen with HOST-F would update the display. Uninstalling the guest additions would restore the display to normal, albeit, non-autoscalling, functionality.

For me, the fix as to enable 2D and 3D acceleration in the Display Settings for the Virtual Machine. After i did that, I reinstalled the guest additions and all is well.

Hope that helps someone.

Take a look at the Known Issues in the "Discuss the 6.0.0 release" post. You may have been bitten by #18205 VM does not refresh, but preview window runs realtime.

Shut down the VM. Go to the VM Settings » Display » Screen. Change the Graphics controller from "VBoxSVGA" to "VBoxVGA".