Our engineers identified an issue that caused our system to stop tracking changes made to calendar invites by customers in Outlook.
Fixing the bug, and triggering a re-sync of the services caused all of these previous updates to trigger finally, even if they were severely outdated or days old.
Although this would have caused a flood of notifications, this would be a one-time side effect of fixing the underlying bug, and is actually indicating that those users who received the notifications are now in a good state.
This could have impacted all forms of notifications including reschedules, cancelations, invitations, reminders, and so forth.
It only impacted customers connected with Outlook.
The issue is already resolved to prevent it from continuing, but old notifications may still be making their way through the system. Please expect some notifications may show up as a result of the above.