I don’t know your whole set-up / procedure but personally where I have messed up with brisket is during the resting phase. I found that once I take it off the smoker (and it reads the target temp and probes right) I needed to let it stay uncovered for about 10 minutes before I wrapped it up and put it in the cambro.
Then once in the cambro you need to make sure the temp stays consistent. Last September the weather was bad and the temp dropped over night down to 39 degrees. We wrapped the brisket and put it in the cambro and went back after an hour and the door was not closed. The brisket was still good but was tight as a rock.
I would also make sure that you thermometers are reading right. The last one I bought reads 7 degrees under what the real temperature reads.
It is still consistent but I have to do the math – 193 = 200. I don’t drink as much beer when I have to use it.