Loosing an interface on a client

[Sungwon Ha]

Hi!

I am having a weird problem on a client side and would like to ask you a 
question. The client (Linux) was successful successfully authenticated using
EAP-TLS and started to have network connectivity. But some time later, the
client loses its interface(ifconfig doesn't show the interface). Any reason 
why my client loses the interface? I know that it is not hostapd access point.
My client is a laptop using 0.0.1 hostapd driver and 2.4.18-3 linux kernel.
Thanks in advance.