You know, there's this other test I ran, and I don't understand it either. I put five thick steaks on the top two shelves. Before I put the steaks on, temperatures matched (vent may have been closed to help it heat up faster). After I put the steaks on, I could repeat these results multiple times:
1) open the vent -> temperatures diverge by maybe 20 degrees (MES reading higher)
2) close the vent and let temps stabilize -> temps match within a degree!
That does imply that something else is going on that I don't understand.
Closing the vent will stabilize the heat, and the element won't have to come on as often.
However when smoking, closing the vent will hold smoke in keeping it from leaving & making it stale. Not a good idea.
Given time they will both stabilize, maybe at different temps, but stabilize.
It takes the Maverick or the ChefAlarm longer to stabilize because they are not connected to a wall, and are therefore moire sensitive.
However like I said before, you can't fault your smoker for it's readings with meat in it---That would be the things you are doing (placement of the sensors, temp adjustments, etc).
Testing while empty will tell you about the Smoker itself.
I hope that helps,