FreeRADIUS and Aruba issues

We are having a nightmare with FreeRADIUS and Aruba AOS8 controllers. Currently we are experiencing an issue where a user can authenticate once on a device and then if they disconnect (turn their wireless off) or after a short amount of time (5-10 mins) they will get disconnected and won't be able to reconnect again at all. The device will either say incorrect password or just generic message that it is unable to connect to the network. A different account on the same device will be able to authenticate and connect again once and will then experience the same issue.

We have an old AOS 6 environment pointing to the same FreeRADIUS servers and configured in pretty much the same way on the Aruba side (all settings are the same apart from ones that might have changed between AOS 6 and 8) and that can authenticate fine.

We have logged ticket with vendor and they have had a look but no ideas currently. Was just wondering if anyone had come across anything similar with FreeRADIUS? I very little Linux or FreeRADIUS experience and another team is currently looking after the server. I have checked the RADIUS client config on the configuration file they have provided from the FreeRADIUS and all seems ok. Is there any other configuration file that would be worth checking from FreeRADIUS?

Thanks