Adding a custom event described on https://confluence.atlassian.com/adminjiraserver073/adding-a-custom-event-861253643.html causes batched notifications to ignore event resulting in no e-mail send on transition with configured custom event.

Also these events are not handled right now:

public static final Long ISSUE_WORKSTARTED_ID = 11L;
public static final Long ISSUE_WORKSTOPPED_ID = 12L;

from what I can see they are used in "Jira default workflow" firing events on some transitions

Workaround:

Turn off batched email notifications and use old email notifications

https://confluence.atlassian.com/adminjiraserver/configuring-email-notifications-938847633.html