症状

1. In People Calendars, no response was visible when adding an event for a user name
2. Despite that they are all valid users, they do not exist in the People directory thus they cannot be added in People Calendars

原因

Just like the People Directory, the Team Calendars for Confluence relies on Confluence indexes. If the index are not up to date (eg. due to a data restore that did not trigger Confluence re-index) then the Team Calendars for Confluence will not be able to locate some users and treat them as non existent users.

ソリューション

How to Rebuild the Content Indexes From Scratch on Confluence Server.