It would help if you could share your effective configuration here to understand your exact configuration.
How quickly are you repeating this test?
There are global authentication timers, how long the AAA session (and this includes guest users) of a device is cached by the controller. Default 5min: https://www.arubanetworks.com/techdocs/ArubaOS_83_Web_Help/content/arubaframestyles/authentication_servers/config_auth_timer.htm
If you quickly disconnect/reconnect in your testing, the controller will resume the previous session of your device and not force it to re-authenticate. This timers can also be set at the AAA profile level to override the global settings.
In absence of this detail in your description, I assume you are using the controller's internal captive portal? Here is everything on the different configuration options for Guest Provisioning:
https://www.arubanetworks.com/techdocs/ArubaOS_83_Web_Help/content/arubaframestyles/management_utilities/enab_gues_prov.htm
If you do not want multiple guest users to share the same guest account concurrently, navigate to the Captive Portal Authentication and select the “Allow only one active user session” option. This will reject a second or subsequent login attempt with the same credentials.
For more advanced guest workflows, I recommend you look at ClearPass.