Hello all,
We’ve experienced in recent manufacturing runs a problem with Pixy2’s onboard flash device not being able to reliably transfer data. This will manifest itself in a Pixy2 that doesn’t produce video on PixyMon when plugged into USB. If your Pixy2 does this or does so intermittantly, please download and install the latest firmware (see links below) which fixes the issue by reducing the flash clock rate. This increases the boot time by a few milliseconds, but fixes these issues.
General firmware
LEGO firmware
Please refer to this page for how to upload firmware into your Pixy2. It’s quick and easy. 
Thanks!