"Looks like someone is on their way" without anyone arriving!
Solution 1:
This tends to happen when there is a connection error when someone tries to use a dodo code to come to your island.
Unfortunately, I don't know what causes the error - I got it when there was a visitor limit reached on the destination island, but there could be many possible causes (Nintendo's netcode tends to be very poor in this regard). Either way, the solution is to tell players to stop attempting to fly to your island until the issue is resolved.