When you create an event and the maximum number of participants is reached, you can then decide to increase the number of registrants allowed.
If you do this, but the deadline for unregistering for the event has passed, then the waiting list will not appear on your event in the back office, and potential registrants will not move to the main list.
Indeed, the waiting list has no reason to exist for an event where no one is supposed to be able to unregister.
So if you want to expand the list of participants in your event and thus increase the number of participants, you will first have to move the unregistered deadline into the future.
