A week has passed since our vendor has called this issue resolved. We have received any recent reports from customers about remaining email delivery issues nor have we experienced them ourselves. This ticket is now closed as fixed. Please open a new ticket if you are experiencing email delivery issues. Thank you for your patience.

Update from our vendor regarding the email delivery bugs:

On Sunday evening, after analyzing many messages we found that there was issue with notifications not making it to the notification service. This issue was addressed Sunday night and reviewed Monday when we found everything was being sent 1:1 Community to Notifications Service. This should not be occurring any longer. 

Good news, our platform vendor has identified the bug causing intermittent email delivery issues and is working on a fix. A rogue node was identified, relating to an indexer service, that was started up on 9/26. Daily and weekly digests should be working as expected - the delivery failure is restricted to immediate email notifications.

I got up this morning to emails, and they've been ok all day (UK), but they stopped again about 30 minutes ago. 19:00 BST - there's four new questions in the community I should have been notified about.

Hi lists, our vendor is reporting this issue resolved as of the morning of 10 Oct US Pacific time. Have you experienced issues since then? Thank you for the last update

I was getting no community emails at all from 6:20 to 14:30 BST today. When they resumed, I think I am getting the right ones again.

But they do seem to have stopped again, about 2 hours ago (last mail was about 21:15)