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I'm currently experiencing this on our 2 Windows Server 2019 guest VM's on a 2019 Windows Server hypervisor. If my Hyper-V connector is closed, when I connect to one of the guest VM's via ScreenConnect, I'm presented with a grey display. Say the VM I'm connected to is at the Windows welcome screen: If I send Ctrl+Alt+Del, nothing visible happens. If I then connect to the VM directly within the Hyper-V host, the ScreenConnect viewer is now live, displaying the login screen (resulting from sending Ctrl+Alt+Del).