So in essence, you had a mixture of THH freebase, ammonium acetate, ammonia, and zinc acetate.
My guess is applying heat drove off the ammonia, setting the THH into an equilibrium with the ammonium acetate with something like 1% of the THH being THH acetate at any given time [no need to do the math for real]. The continued heat drove the ammonia out of this equilibrium, letting more THH react with more ammonium acetate. And again and again until you had a beaker of THH acetate and zinc acetate.
I'd agree with your plan, add a squirt of vinegar to bring the pH <7 and manske it.
Alternately, if freebase is desired as the end product you should be able to just base it with room temp ammonia and this time filter the solids.
With the exception of the first one or two manskes when extracting seed, I've mostly only got trouble from working with harmalas in heated solutions.