You didn't mention the Egg temperature so it's hard to tell if 12 hours was long enough or not, but I agree with the esteemed Mr. Grail. It doesn't sound like it broke through the plateau. here is a point where the big cuts like butts and briskets stall and the internal temp stops rising and can even drop a little. This is when the magic happens. The internal collagen and connective tissues are rendering and that can take a while.
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