It sounds like there are a few different problems that result in similar manifestations. I would like to consider these separately so that I can focus in on one area at a time. In summary, we are seeing these behaviors:
@truckmann - WiFi network connection drops and never recovers. Starts working after a power cycle.
@SLOBrewer, @emdubeu, @jshufelt, @johnholzerjr - WiFi network connection is fine, but no data is logged.
@ecotony - There is a 10+ minute delay between starting a session and seeing data, but it eventually started. Device lost authentication and had to reactivate.
Is my understanding correct?