We have an "epidemic" problem with XBEE Wifi modules.
Over 1 week 5+ modules have become unresponsive.
At first the modules work flawlessly, but at some point after powercycling, they become unresponsive.
We then place module in Digi dev board, and observe the following: Module will accept firmware upgrades, but only version 101x will give us back command prompt.. 102x versions cause module to become completely unresponsive (even to break+reset procedure).
When running 101x versions we dont get a connection to the Access Point (WPA2), so that is not a work-around.
We have 1000uF cap on VCC. System is powered by 3.6V lithium, running around 3.3V, but even with 3.3V bench supply attached, symptoms above are the same.
PS: We also run XBEE PRO modules in the same hardware and these modules work flawlessly.