The On-Demand 5.5.90 update included a few changes to the Events report and the Events widget in the Communication Center, as described by the inimitable Doug Peete in this handy article.
In short, events are now listed by the subject of the notification email, rather than the name of the communication plan on which the event was based. This allows you to quickly identify the key information in each event (provided you have followed best practices when creating your email subjects) and easily adjust how events are displayed. (Events injected via an event domain, such as older integrations, will continue to display the name of the event domain and the event ID.) If you have not specified a subject for email notifications, the report will use <No Email Subject> as a placeholder and a reminder that you're missing out on a pretty great feature.
One part of this feature that may trip some people up is that events that were already in the system prior to the update will not have an email subject OR communication plan name - they will simply display <No Email Subject>, along with the form name.
This is because older events did not store the email subject as an event property. Instead, it was generated during notification delivery. Attempting to regenerate the email subjects for historical events would be a considerable performance hit and would likely make the Events report unusable.
This feature also inadvertently removed the event domain and incident ID information from existing events based on event domains. These events are also showing "<No Email Subject>"; this is a bug, and we'll address this as soon as we can.
This only affects events that were already in the system prior to the 5.5.90 update: all new events will display the correct email-subject-and-form-name/event-domain-and-incident-ID combination.
xMatters internal reference: DTN-4814, SUP-12387, SCO-7112