Apple Devices & WiFi:
So everybody knows that Apple has its own opinion for WiFi Roaming and switching to the next AP with the best wifi signal. I think it's a good idea to implement the 802.11k standard to Sophos AccessPoints, according to the knowledge page from Apple at: https://support.apple.com/en-us/HT202628 where they talking about the 802.11k Standard. Maybe this is a solution for Apple devices that have connection issues and do not want to switch the access point.
Ryan Donohue commented
I second this. Lots of issues with Apple devices roaming on Sophos wifi.