Emails are not sent immediately after coordination issues are created. Instead, the Assignee of a coordination issue will receive a digest email on the hour listing any coordination issues that have been assigned or reassigned to them. For example, if two coordination issues were assigned to the same user around 2:45pm, that user will receive one email at 3pm that lists both issues.
Users who are mentioned in a coordination issue comment (using the @ symbol in the Activity panel) are immediately sent a notification email containing the comment and a link to the issue. See Mention Users in a Coordination Issue Comment.