I don't know if it were the intended behavior. But the IPTV Channel (Video Bookmarks) Plugin allows an administrator to add an IPTV feed. But, no other user can see the feed, only the administrator. Since you can only add feeds from the admin back-end, then no user besides the administrator can ever use the plugin. Am I correct in arriving to this conclusion?
In any sense, if I am correct on this plugin's behavior, I went ahead and removed the user_id parameter from the .cs file where the query is made. I compiled it and uploaded it to my instance of emby-server and so far it's working great.
If this is something anyone might be interested, I can do a pull request on the Github repo to submit my change. Or if there is a more appropriate place to upload my code changes, I can do that as well.
edit for grammar