I use a freshly installed Volumio (based on Debian) instance on a Raspberry Pi 2 Model B Rev 1.1 equipped with an Edimax EW-7811Un USB device to get WiFi. Power is supplied from a HifiBerry AMP+ sound card fitted onto the Pi. The WiFi signal is very strong.
But when I cold boot my Pi (meaning the Pi has been turned off for hours) WiFi doesn't work. The Edimax device blinks blue on and off with a steady rhythm. While such blinking usually constitute an error indication, the documentation fails to mention it. If I also use Ethernet cable and run
lsusb I see that the Pi does recognize the USB device correctly, yet it's not working.
I pull the power from the Pi, wait 5 seconds, and then turn it on again. Then WiFi works!
The problem can be replicated if the Pi gets enough time to cool off. What does this suggest? Hardware problem with the dongle, or the Pi? Is there something I can do with software to attack the problem?