Symptoms
After upgrading to 4.6.10, the notifications for a Default Client Event are not being sent.
Diagnoses
One of the fields within the body of the email was causing an error that was preventing the emails from being sent.
Resolution
Deleting the bodies of the notification emails allowed for the emails to resume being sent. After slowly rebuilding the emails, one of the dynamic fields within the email was revealed to be causing the issue. Fixing the implementation of this field fixed the issue.
