This weekend I upgraded a Jira instance from one LTS release to the next (8.13.1 to 8.20.1).
Everything appeared to go well, but shortly afterwards users started complaining: Jira is not emailing certain users.
I checked, and sure enough: there's a situation where Jira 8.13.x and all prior releases would email, but Jira 8.20.x will not.
Specifically, this affects users like this one, who are not in a group like jira-users
blessed with 'Application access':
What should happen if a new issue is created, assigned to 'helpdesk', or with 'helpdesk' as a watcher?
helpdesk@mycompany.com
The 8.20.x behaviour is actually correct. An account without Browse permission shouldn't get emails. Yet this important bug fix is not listed in the release notes, nor in the [174 bugs fixed between 8.13.1 and 8.20.1|]