I have a problem similar to yours:
Also I can not connect after an interval of 2 or 3 hours, the need to reconnect VNCServidor uvnc_service restart the service, ie manually, already tried several ways but without success.
It's like you said, after a while it loses the connection!
I do not know what to do.
That VNCViewer the small screen is "Nogociate Protocol Version ..." and never leaves it .