Hello,
I am not sure if you already found the solution, but here i want to share how i am doing.
1. In the Captive Portal, you can see the connected clients.
or
2. Open the Log viewer and select Radiusd category, in the filter type Login….. it will show you all the login related entries….as soon as any new user is authenticated on the system, in the log it will appear.
Hope this helps
Ilyas