Moderators - you can delete this post or leave this response for other that may stumble into this.. After a lot of head scatching I finally located the issue. Microsoft downlaod some sort of Movies and TV app automatically on my Win 10 Pro system. It was interferring with PBX. I just happened to stumble on that VLC or FFV wasn't playing MP4 videos by default anymore. Once I found out what was going on I was able to fix things by running
Powershell
Get-AppxPackage *zunevideo* | Remove-AppxPackage
MP4 vides are now playing fine again. Sorry for the false alarm.