iPhone edge client problem

Hello!

i have strange strange bug with f5 Apm. I configured apm with certificate verification + ad + radius.When i'm trying to connect from pc all working fine, authentication passes well. But when i'm trying to connect from iPhone or ipad it's failing with authentication failed. In report about last session I learn that client send nothing in username even if it asking about it while connecting. Where can be error? I got latest version of big-ip and its hardware based.