Wifi issues with atheros mini pci wifi card / pfsense nanobsd 2g 2.0

[fiftyheight]

Hi,
Come from a pretty working well 1.2.3 nanobsd installation on my alix 2D13 board.
Since i update my box to 2.0, i have issues with, i think, my wireless lan (used in AP mode), wifi card is compex wlm54sag with atheros chip
It become randomly unreachable, and when there is heavy wifi load (ex when a wireless client runs a bittorent client with 3000-4000 states / 1MB/s download) the pfsense box simply crash in about 10-15 minutes and i have to cold restart it (sounds like kernel oops or something like that).
If there is no heavy wifi traffic, this is just wlan interface wich seems become down. On this situation, /var/log/system.log shows me several

kernel: ath0: ath_rx_proc: no mbuf!

and then when i try to ifconfig down then up ath0, it's showing

ath0: unable to start recv logic

and i don't know other way to re up the wlan interface than reboot the box

I tried to reinstall nanobsd image from scratch without restoring any backuped configuration, i got the same

I showed in forum some topics whith that kind of issue, but they are pretty old, and nothing about pfsense 2.0

I don't know other way for fixing my issue other than downgrade to 1.2.3, anybody have suggestions ?

Thx