That same WiFi bug – the one I told you about that’s affecting some HTC One S and international One X handsets – is also plaguing the AT&T version of the HTC One X. It was subsequently fixed in OTA updates for the One S and the international quad-core One X, but, as we know, AT&T likes to take its time before releasing updates.
HTC’s temporary work-around is to toggle the connection on and off, which will allow the phone re-register on the network, fixing the problem “for a while” until the phone decides that it wants to stop working again.
I’ve experienced this problem myself, and originally thought something was wrong with my router. While toggling the WiFi on and off did correct the problem for me, I’ve also had success in setting the connection up as static (see my previous post for more information on how to do that). Even though it’s an easy problem to fix, it is my hope that AT&T will get its act together and push this fix out ASAP.