I had a similar issue just after Christmas with a system that has been running fine for three years. I upgraded from the ZD1050 to the ZD1150 and student laptops where taking upto 30 minutes to login with no access to network or internet.
The eventual fix was this.
Thank you for contacting Ruckus Wireless.
We have seen some issues where the laptops takes some minutes to logon to the network to gain access, so in these kind of cases we have found that forcing the Kerbos authentication via TCP instead of UDP, across a layer 3 routed interface is fixing the issue. So I would request you to visit the below link and try it on couple of laptops/machines and let us know the outcome.
How to force Kerberos to use TCP instead of UDP in Windows
You can do it manually or by using the 'fixit' application. I would suggest you to perform manually on one machine and 'fixit' application on different machine.
This worked for us after some really thorough testing.