It is not uncommon for the smoke to be heavy, and
white, at the beginning of a smoke.
This is NOT the wood catching fire! As the wood starts to smolder, it will put off the heaviest smoke, which will taper-off. Now, it the smoke turns more gray, the box temp spikes and it smells a lot different, you probably have combustion. If the latter doesn't happen, don't sweat it! Just set the thing, go enjoy something else, and come back when the meat is done.
I hear folks talk about the constant TBS of the AMZNPS, and I get it. However, with wood chunks, in any powerful electric smoker, they will definitely smoke heavier at the begging. As the smoker goes into a "maintenance" mode (temp is reached, and the element pulses to maintain the set temp, and is no longer at full-power), the wood will "settle-in" and give that TBS everyone is so concerned about. Nature of the beast. I have watched my smokers do this drill for years, and haven't had bad BBQ yet! I've also never had wood wrapped in foil catch fire - even the dry stuff.
Btw, if you
do get combustion, it won't last long, and will put itself out
if you don't open the door! Don't give it that big rush of oxygen to make it worse. It will die-down, on its own, and will not effect the taste of your meat.
Just my 2¢....