Issues with hit and miss email notifications sometimes are related to whether you have a valid DKIM record and SPF for the sender email. Do you know if this was installed in your LMS for your sender email? May be worth checking. 

Something else you can check is to make sure you test user and faculty account are in the branches or groups you ave aligned to the notification - they probably are since the onscreen notif came through…

Last resort is to open a ticket with support so they can assist.

SPF, DKIM, and MX are all configured correctly in the email sender domain.  Configured and tested it myself; green checks across the board. 

Like I was saying in the original post, emails for other notifications are working fine, it is just this one that is giving me grief.

I’m going to log a support request as it just seems something odd is happening on the backend in our environment for this one notification type.

When you test, do you use test accounts? If so, perhaps one is configured as a PU and therefore would not get the notification...something to check...

Already checked that.  Doesn’t make a difference what type of user it is.  checked the branches and groups as well.

After checking with support it turned out to be an extra space character at the beginning of the From email address in the notification settings.

Also interesting is that if you use the first_name shortcode in the email being sent you get the first name of the learner submitting the assignment, not the first name of the instructor receiving the email.