Welcome to the Nexus!

You mean 0.5% yield btw..   Where is the bark from?

I think 100ml naphtha per 100g bark is too much naphtha, it might not be saturated enough and hence why you are not getting big yield (unless you have bad bark).  Hopefully you didnt throw the naphtha post-freeze away and are reusing it or having it stored?  I would suggest evapping it down to a third of original amount and then freezing it again.

Good luck and dont throw the whole bark away yet, keep pulling, use smaller warmer pulls maybe. Good luck!