Here's what happened. I know because I've done it before. First know what probe tender really is in the thickest part of the flat and from your last set of pics, it looks like you wrapped it up in a blanket and it continued to cook until it was overdone and that's the reason it flaked.
Reading what the folks are doing here, I've found the brisket end game is all important. Once I pull one at probe tender, I'll let it cool down loosely tin foiled until the IT is about 150*F. That may be 1.5 hours.
Just some FYI. I'm no master at it. On the up side, bet it tastes great!
One more thing, I'll never again do a packer brisket that is not Choice or above.
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