5a693e87_Plus__known_issues____RealVNC___Workaround
[ID] 137 [Description] VNC Viewer Plus may not be able to connect if a host computer was shut down using its physical Power button. [Status] Won't fix. [Workaround] 
Shut down using VNC Viewer Plus power management tools, or via the host computer's operating system.
VNC® Viewer Plus (known issues) - RealVNC®
Workaround