I am having a similar experience.

per 100g mhrb basis

I am using

100ML 5% vinegar

mix for 20 minutes

120ML hot water mix for another 10

95gram pickling lime.

I then use naptha as you, warmed up solvent, with the plate of bark over boiling water and mixed for 10 minutes before filtered into a jar and then poured onto a glass plate and freeze precipitated.

I have done 7 pulls totaling 3.3G of this same bark in a week and a half.

I have done evap test on my solvent evaporates clean. the final product is 100% dry white powder crystals, no discoloration or anything. I usually only get 1.5-2g off 100g, only thing I changed was

the amount of lime I used, 95G opposed to 60g