Hi Phil,
This is a known issue CFD-7041 now. iOS 15 comes with a new DHCP fingerprint "1,121,3,6,15,108,114,119,252" according to the log.
Log snippet:
{
2021-10-14 15:42:42 info ah_auth: aaa: station(626a:7df3:ce48) option 55:1,121,3,6,15,108,114,119,252 no mapping os in database
}
Until this is enhanced at the XIQ side, you should be able to work around the issue by using a S-CLI with the following command or adding a custom OS object at the XIQ side.
os-version "Apple iOS" option55 1,121,3,6,15,108,114,119,252