Holly, hoping you're still taking notes to add to that list.
This one is rather technical, as it involves a key component of the notification mechanism, and a consequence thereof. It is definitely a core developer community element to be fixed rather than a configuration.
Notifications use a LIFO notification queue (last in, first out). It also has a throttled queue to not overload e-mail systems and reduce the risk of all the notifications triggering a spam alert.
This means that if there is a lot of activity, older notification can be delayed for (from experience) the better part of a day while the queue slowly clears as it is being constantly refilled.
Two improvements would help here.
- Change the queue to FIFO (first in, first out) so notifications arrive in the order they are raised.
- Have user action clear the queue - if a user gets a notification, comes to the site and clears the on-site notifications, all of those that are still in the e-mail queue waiting to be sent to that user should be cleared, so the user does not get renotified about things they have already seen.