This issue was reported August 4th and was since resolved. Reports came in that invites were not being sent to prospects and that other email services, including reminders and notifications were not functioning. Our team determined that invites (meetings on Calendar) and notification emails were not sent to a subset of our customers during this time, and these meetings / emails are not recoverable. Meetings booked during this time may not have appeared on the prospect / assignee calendar.
The cause was that one of our new web services connected to notifications failed silently.
Our Site Reliability Team was able to resolve this issue as of 2:30pm EDT August 4. We have implemented further monitoring for this and other services so that if any impacting issues occur in the future, we will be able to mitigate the problem quickly and without user impact.