wifi not recognized unless restarted in archos 32
As a power-saving strategy, radio chipsets can sleep -- meaning they stop actively listening for a wi-fi network to connect to -- when they are out of range of any network, and will wake up to search for a network once every few minutes.

It may simply be that the radio on your Android is doing this, and that you haven't waited long enough for it to wake up once you come back in range of a wi-fi network.

A quick search tells me there's a Powersave disabled setting in the wi-fi settings on the Archos that might help.