From the looks of it, the client is changing WLAN and then the association request is being rejected. You could test by enabling fast-ssid change, which allows you to switch between WLANs without delay (the WLC enforces a delay by default, this could be the cause).
config network fast-ssid-change enable
(in the GUI, Controller > General > Fast SSID change)
If the iPad is bouncing between the networks, than that is likely an issue with the iPad wireless supplicant behavior. The error message in red above is likely due to the device switching with fast-ssid change disabled.
So, if we are more concerned with why the device keeps moving between networks, we should capture a bit more data. Running a longer client debug should give us some additional data points.
I've seen similar behavior with Apple devices when they "Remember" wifi networks -- sometimes you need to "Forget" other networks in the area to stop the device from associating to it automatically.
Also take a look at user idle timeout on the controller, increasing this feature from the default of 500 seconds will prevent the client from being deauthed/dissasociated while the client is dormant. Depending on the size of the network, you can set it to something like 1hour or more.