If a plugin uses \core\notification to display information to users whilst they are adding or updating an activity, then notification then also appears on the course/defaultcompletion.php page:

In the above example mod_choicegroup displays a notification via the mod_form.php page to indicate to the user that the configuration would make no sense because there are not groups.

The 2nd notification is from an internal plugin that requests data from a 3rd party server and then displays the results on the form for the user to select a value from.