On my Unifi setup at home with multiple APs I had to disable 802.11r to get things to roam fast. I have Android and Linux laptop, wife has iPhone and MacBook.

With 802.11r on, things would disconnect for 60+ seconds before reconnecting. It was a constant frustration of "arrrrrrrggghhhh fucking connect damnit I'm standing a meter in front of the AP can't you fucking see it fuck fuck fuck just connect, it's right THERE, connect NOW, arghhh" and then it would completely disconnect (no wifi found) and then reconnect a minute later.

With 802.11r off things just roam smoothly. I guess the people who inventned the tech didn't test it thoroughly enough.