I don't know, but think your problem may have been opening the smoker door. In so doing, you let the heat out of the smoker box, and the remaining hour might have been spent trying to get the box back to temperature, though that seems an unusually long time. I would check your wall mounted temperature sensor and make sure it is clean (if not, it easily cleans with a wet rag or paper towels), and maybe next time, if you have a thermometer that monitors box temp as well as meat temp, run that as well and see what is going on.
The good news is that you had a tasty meal. Congratulations.