Mite problems

[nachash]

There's a ton on here about mites already, not to say your question about repti-bark carrying them, or your overall issue isn't pressing.
I have used repti-bark without problems of mites for about 4 years. Mites are an arthropod designed to survive just about anything, so to say that it is impossible would prove to be impossible. But it would be better to think about where they likely could have come from.
All parasites have life cycles closely tied in with their hosts. There are also requirements for populations to start out with a particular threshold in order to get to critical mass (infestation).

Likely answers, they were on the snake in numbers too hard to tell, and grew larger in population over the past month. Or you maybe have supplies that were used and not fully disinfected (when I had mites it was due to that and I paid for it with hours of scrubbing).

This is one of the things in life that follow the adage of ounce of prevention > pound of cure. After a month you should do a full cleaning anyways, a weekly light cleaning, and daily spot checking. Next some like the prevent-a-mite and other chemicals. I find taking the snake out, giving it a bath while using a cotton swab with mineral oil gets mites off the snake (make sure to check facial pits). Now put the snake in a temporary enclosure, then go to work on the habitat. I mean go to work, bring the dogs of war, go nuclear with bleach 1:10 ratio to water. Rinse until you can't smell bleach, and until you are sure you haven't a mite in the world on your snake's proverbial shoulders, go with newspaper or paper towel for substrate.

Cheers

p.s. mites appear to give the same symptoms to snakes that lice give to humans, so I imagine the snake is pretty annoyed. Stress in reptiles is a hazard like any organism. So good luck!

p.s. Pitch the used rept-bark and make sure to wash ALL cage equipment and decor. Bleach is safe if used properly, ensuring the enclosure doesn't have bleach remaining. All chlorine will evaporate with time, so if worried just wait until then, rinse out again and dry.