Quality control is the baghouse complaining to the loader operator that the splinters are poking thru the bags.
Most operate on poured concrete slabs, but ramp up in spring and dump raw materials everywhere. Loader operators scoop too deep full of rocks and bugs,dump it on chipped pine instead of the hardwood sawdust. Then bake it half as long in warmer temps during busy season. The pine decomposes at a different rate, and the bugs hatch just as you open the bag at home and sift the rocks out. Another loader operator may have a better eye and experience and turn out perfect batches from the same plant.
I'm done with pre mix, just do ProMix or Peat and make my own with perlite, Espoma and a few additives.Or buy the stuff thats been buried under snow all winter stored in the back of the garden center, thats aged nicely with the rocks.
Edit* Holy crap, thats all wood and no peat. No wonder quality is all over the place with that stuff. The different trees composting together will never work without time. At least with peat there is a more definite PH and rate to start with.