There are so many things that slow people down at fastpass return it's ridiculous.
First off, you have the people whose bands for some reason register slowly. The light on the mickey head on the pole spins for twice as long as other though does eventually register green.
Then you have the people that think that just by having the bands they get fastpasses to everything. So they scan their band, get denied, and then you have to explain to them that they have to use the app or go to a kiosk to actually schedule a return time. This is especially fun if the guest doesn't speak english.
There is also the fact that some children are too short to actually reach the mickey head on a pole meaning that the parents have to both lift the child and finagle their wrist to try to get it to register. Brilliant. Children that are tall enough still have trouble aiming their bands which again slows everything down.
Similarly, you have the people that aren't wearing their bands for whatever reason and have to dig though their ginormous purse/backback/suitcase/cooler/what have you in order to find it. Of course it's always on the bottom and of course the people looking never step aside to let other people through. Because it was their turn and they're gonna be next or else.
Finally, you have the people whose entire's party has magic bands that won't sync up to the app. This is the worst because it's totally not their fault yet the problem takes the longest to fix. Usually what happens is that the mickey head turns blue and then tells me that they're scheduled for a different ride or different time. If that occurs and they dispute it, everybody in the party scans their magic band to see if the same thing happens. If somebody turns green, the entire party is let through on the assumption that the entire party did schedule their experiences together and the app just screwed up. If nobody scans correctly, somebody in the party has to pull up the app on their phone and physically show that yes, they are at the right attraction at the correct time but their bands are just stupid. Finally, everybody has to scan their bands again so that they can be granted access and not be given any trouble at merge.
I will say that when the magic bands work quickly they are pretty nice from a CM standpoint because we no longer have to play the "why is this fastpass wet" game nor do we have to touch any papers that tourists decided were a good idea to store in their sweaty gross bras. Because that happens. Unfortunately, I can scan a paper fastpass with my eyes four times as fast as it takes a band to register on the podium which when we're busy does make a difference in how backed up our line gets.