I finally have this fixed. I don’t know if it will help anyone else, but I deleted the PLEX Server app off my Synology NAS and added it back in. Once I did that. All users could see the server and libraries again, and I was able to delete Managed Users which had also stopped functioning.
Doing this brought my PLEX Server back to version 1.16.5.1552, which was the last working version I had before updating to version 1.18.x
I am see no reason for me to upgrade so I will leave it alone until I am forced to upgrade.
Thank you all for your efforts in trying to help me get his going again.
