Unable to play any video
If it first you don't succeed, reboot. I forgot the first basic rule of troubleshooting Restarted the box and now all is well.
Server: Synology DS916+ with Plex Cloud Mirror
Local Clients: Apple TV 4K / Roku 4 / XBOX One X / PS4 Pro / Nvidia Shield / Google Cast
Primary Interface: Vizio 70" M 4K / Sonos Playbar + 2xPlay1 & Sub / Nvidia Shield / Harmony Elite
Mobile Clients: Nexus 6p / iPhone 6+ / iPad Air 2
Remote Clients: A dozen or so friends and family members, mostly using Roku 3's
Network: 1GB Fiber