I have 2 whisperers and have the same behaviour from both.  One worked for a few months and then failed.  The second one is brand new and never has worked.

For both devices I have done the full reset many times.  The reset and subsequent setup appear to work.  The Whisperer connects to the network and I can change the LED colour (so I know my phone and the whisperer are talking).  I then power off the whisperer and turn it back on for a transmission test.  The device powers on, the LED comes on and then within about 20 seconds the LED turns red and the unit shuts off.  This is supposed to indicate that the whisperer cannot reconnect to the network (and that I should move closer to my router).  I moved it right up to within 1 foot of the router and still cannot reconnect.

The fact that I had 2 of these and neither works suggested the problem was not with the devices, so I replaced the router with a high end Asus Zenwifi mesh network.  This still did not resolve the problem.

I do not believe I have a battery issue.  The units have sat in the sun for about 6 weeks during this testing.  The support documentation in 1 place says the setup must be done within 20ft of the router and in another place says the setup must be done within 20 feet of the sprite.  I've tried both and in both cases the setup appears to work properly. But in no case can I reconnect to my network after the unit is set up.

Both units are hardware version 2.2 and firmware version 2.2.0.  My app version is 2.5.3.  Server Status reports OK (response time 1.0 s)

Any suggestions for what else I can try?