5a693e87_Plus__known_issues____RealVNC___Workaround
[ID] 149 [Description] VNC Viewer Plus may not be able to wake a host computer from hibernate or standby mode if the operating system has requested that the Intel AMT graphics driver power down. [Status] Won't fix. [Workaround] 
Disconnect and then reconnect.
VNC® Viewer Plus (known issues) - RealVNC®
Workaround