After upgrading our Virtual SmartZone and all AP Zones to 5.2, we ran into an issue with the Captive Portal on our Guest SSID's no longer working on R730's and R610's. I don't know if any other model had the same issue, but after downgrading the AP firmware back to 5.1.2, Captive Portal was working again. We had tried factory resetting the AP's, moving them to a different controller on same firmware, deleting and re-creating the SSID's, etc.
Support is working to replicate the issue, but wanted to make sure people knew what we ran into in case you see it as well.