I am having the same issues here with ios 10. I have not had any luck figuring out why they are getting disconnected but I have also noticed that if a user is connected and then moves to a different area of the building where they would connect to another access point, they can’t connect on the new access point and have to go through the entire onboarding process again. It only stays connected if they are connected to the same AP.
One other interesting thing I found was only users who have previously been onboarded and then upgraded to ios 10 are having the issue. New users/devices already running ios 10 that are onboarding for the first time are not having an issue. This leads me to think there is some type of mismatch in the certificate. However, even if we remove all certificates from the system and have the user remove all certificates from their device, they still have the issue.
Anyone else have more info or a solution? I did find a link giving some possible solutions but I'm waiting for a user to try it and get back to me. Here's the link: http://www.valuewalk.com/2016/09/ios-10-wifi-issues-fix/