Thanks for your replies Jim,
I've done the following and still not working:
1-Restored the fresh Win10 and JRiver fresh install (from Acronis Disk Image), with no antivirus but (Windows Defender default) still not working.
2-The install was already on Red October Standard (Default), but I also ran the "restore default settings.bat" file, rebooted and played the movie with Sync problem.
(The Red October HQ plays a black screen with the audio only)
Let me add the following,
The out of sync Video happens rather quickly, after playing about 5 seconds of movie.
So far happens on MKV files only (a few MP4 do play fine).
The sync problem happens only when on "Fit Window" or Zoom greater than %150.
I after the fresh install in Win10, I loaded a JRiver local library created previously on Win 7.
I am keen to try any other ideas please.