Thank you! 
Blockquote The Shield comes with older versions of the Plex client and server apps pre-installed. You need to update them through the appstore before continuing.
Done! This was news to me, but I realized this during my troubleshooting.
I did uninstall both the Plex and Media Server apps. I had to go into system apps to find the Plex Media Server app to uninstall it. One weird issue is the Plex Media Server app does not appear to uninstall from the Shield even when I select uninstall from the system. Witness screenshot below on my 3rd attempt to re-install:
https://imgur.com/a/EjEUjxL
What I found is what you guided in instruction. I needed to remove the servers from the Plex web app itself. Thank you so much for this instruction, it did not occur to me that this control was set at this level. I have gone through and re-set all my libraries from the Plex web app and removed the older settings.
I am going to wait for the Plex dance to occur and see if this resolves my problem.
Blockquote Synology - it’s possible they don’t allow using the admin account anymore. Go ahead and add your new login like you did before. Then on the Shield, you’ll need to mount/remount the connection to your Synology.
Yes, that’s what I was wondering but there is no place on the Shield to modify the access credentials to the Synology NAS. This is what tripped me up when I made the change originally. I think I’ll just leave it alone if I get it working again.
Many thanks for your support!
