The connection via Ethernet doesn't work after a while, again and again [solved]

sonnyyu:
The upgrade from hotplug2 to standard udev might be work around to fix AR9331 has a hardware bug where spurious RF emissions affect the USB PLL. Nothing to do with wifi connection but USB stability issue.

OK, I got it.

sonnyyu:
The better method is use kernel r39212 and later which has patch (work around for USB stability issue.) , or replace AR9331 with new revision one which the hardware problem is fixed ?

What issues can I face relating the USB stability? Where I can know more about?

What about the original problem?