I've been using Wixels without problem for a couple of years now, but have just managed to fry 3 in fairly quick succession. Not only is it getting expensive, but I'm no closer to working out why.
The application is a 2S lipo battery powered mobile robot (battery voltage measured at 7.9v on the last occasion). The Wixel simply performs wireless comms for an on-board 3.3v Arduino. The Arduino is powered directly from the 2S lipo via its RAW pin and works reliably.
The Wixel can only tolerate 6.5V on VIN so a Pololu S7V8A regulator is used to supply a regulated 5V from the lipo. The regulator has a 47uF capacitor between its GND and VIN mounted as close as possible, as recommended.
Aside from GND, the Wixel only has two other connections to it - P1_6 (Tx) and P1_7 (Rx), which are connected to the 3.3v Arduino's Rx and Tx respectively via 10K current limiting resistors.
Wixel failure mode is that the green LED goes dim and the main chip starts getting hot. It still outputs 3v3 so I think the on-board regulator's OK. Each Wixel seems to have failed on power up rather than whilst running.
The only other suspect would be current/voltage surges from a DC step up module also connected to the lipo to provide 12v. However I've measured VIN, Tx and Rx on a scope during 'normal run' and can't see any noise. I've also looked at them during start up and they all ramp up smoothly over a few ms.