Bark settling to the bottom is normal is the heavier material will always separate itself out with gravity.
When you mix your lye with your water, as long as you mix everything until it basically becomes clear water again, you've fully dissolved the lye. I usually dump it into a mason jar, close the lid, shake for a minute, and then set down open the lid to release any pressure resulted from the exothermic reaction.
I know that "foam" layer you speak of, or at least I think I may have an explanation for you. I believe this layer may be plant cells and fatty cells and other alkaloids collected from the extraction. Having that in your mix will not hurt, it's the brown soup that you do NOT want any of in your freeze jar/evap dish.
Also, pulverize the root bark more. It'll make it easier for the soup to break everything down.
My final suggestion would be to lessen your naphtha from 75ml to 50ml respectively. This will make it easier for things to crystallize during the freeze precip. You said you did two pulls, I would actually do 4, and with even less naphtha, maybe even 30ml - 40ml per pull?
Just some suggestions from my little dark neck of the woods!
Good luck!
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