When this occurs you should try enabling debugging for that particular device mac address and see if you can more information :
logging level debugging user-debug <device mac>
You can also run the following :
show show auth-tracebuf | include <device mac> --- This command will give you an overview of whats going on with the authentication process
What Radius server are you using ? You should also check the logs in the radius server to see if there's any error message
What AOS version do you have installed ?
Does this also happens if you disable the wireless NIC or it just happens when device comes from a doze state ?
Note: Make sure you disable the debugging when you are done troubleshooting : no logging level debugging user-debug <device mac>