I just added more spots to my event. Why aren’t all waitlist players being notified?

Even if 4 new spots open at once, the system is set up such that only one person gets the notification at a time (those 4 spots are held for one person at a time).

Spots open up to waitlist players one-at-a-time. So, if you opened up 4 more spots, the first person on the waitlist will get a notification. If they declined, or only took one, two, or three spots then the next person will get the notification that there is a spot (or spots) open for them.