Wison,
Pick as user that is not able to authenticate and enable debugging for that particular user
config terminal
logging level debugging user-debug <user-mac>
As mentioned in the previous post, it would be beneficial to look into the event viewer of the RADIUS server and check for the users that are not able to authenticate. The event viewer should have an event for authentication response.
Also, as mentioned by Sathya, run the command "show auth-tracebuf" command that will show the sequence of steps for the user authentication.