Stirring with naphtha for 12 hours seems rather excessive and is likely to have produced an emulsion, with the aid of the bark particles. A few minutes of gentle stirring would have sufficed.
Have you tried looking up 'emulsion' using the search function? There are a few tricks to breaking emulsions, all of which have been described repeatedly on the forum. One easy one to try is adding more lye.
150g bark is quite a lot to be committing to a (first time?) extraction. 50g or even 25g would be a better amount to practice with. One of the problems is the difference in scaling of surface area compared to volume, which is crucial in the extraction environment.
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