I burned a couple days on this.

My email configuration was correct. My OP settings were correct.

I could send test emails and account update emails correctly and received them perfectly; however, when I updated a work issue in some way, no email was received. In fact, I could see no attempt to issue mail at all the logs.

It turns out that my registration email was mixed-case, ala UserName@example.com.

I noticed the following in the logs (with debugging turned on)

SELECT “users”.* FROM “users” WHERE “users”.“type” IN (‘User’, ‘AnonymousUser’, ‘DeletedUser’, ‘SystemUser’) AND (LOWER (mail) IN (‘UserName@example.com’))

That was my only clue. So I made my email address all lowercase and voila, email notifications worked.

I hope this saves someone some aggravation. Probably should be a bug.