If the left side has a higher air flow rate, it could be evaporative cooling of the sticks... Is the air temp higher above the firebox or can you tell... There are so many things happening inside a smokehouse... circulating air currents.... humidity differences...
I've been inside commercial SS smokers that had 5,000 #'s of meat hanging in them and the operator knew exactly where the cool spots were... Those were the go to areas to check for final temp on the smoker load... Those smokers had HUGE recirculating fans to try and equalize the temps and couldn't do it..
30 degrees is a bunch... I know that will keep you awake at night trying to figure it out....
One thing to try is..... Adjusting where the heat/smoke enters the smokehouse... sometimes making adjustments that seem WRONG can fix the problem.... That's the way it goes for me at times.....