Nothing to tell.
666 is subscribed to content from these users. Their content will appear in the activity feed.
These users are subscribing to 666. 666's content will appear in their activity feed.
Go to https://www.zapread.com/Messages/Alerts/ and click on Go to Post of an alert with the title "You received a tip!", you will see a 404.Maybe add a link to the other user there?
Fix for this should be rolling out now.