Nope. I'm an experienced kamado user and I do not open my lid very much at all, nor make big adjustments to my vent settings or anything else. "If you're lookin' you're not cookin'". I typically open my grill for smoking briskets and pork butts 1) to put the food on. 2) to wrap if I want to wrap. 3) to take the food off. In this case I was doing brisket and pork butt at the same time, so I was opening the grill a little more often (wrapped brisket and pork butt at different times and of course one meat was done before the other). I'm guessing it's because when I was wrapping the food I left the lid open. The temp rose and stayed around 300 for the rest of my cook, so I do think you are right that I fed the fire when I opened the lid for a couple of minutes which is a pretty long time with as big of a grill as this is - that's letting a ton of air in. The image below shows you where I set my damper on my billows for low and slow, even in the big 'ol 42. I only open this 2 or 3 clicks which is about double the opening when I'm doing 275.
I may not know where my top damper should be. Maybe I could have closed it just a bit more. I know where mine needs to be too for low and slow- been very successful at 225-235 and the grill staying very low and fully heat soaked on long cooks. It's just those mid temps. It'll hold 350-375 rock steady and won't rise much. It'll hold low and slow. I just haven't gotten it dialed in yet at the 275 temp. I feel like it always wants to be at 300. Which isn't a big deal - like I said in my original post it's in the ballpark.
I will try to figure out a system where I'm reaching in and grabbing a piece of meat and closing the lid back quick while I'm wrapping my food, then opening it back quickly to put the wrapped food back on and see if that helps.
Look man, I'm not knocking the product - it's the best product I've ever used - by far. ESPECIALLY for grilling - well and smoking a HUGE amount of food in an actual Kamado - I mean there's nothing else you can use that cooks as much food and isn't a stick burner or a huge rectangular box of an electric smoker or something. I'm just saying "temperature control to a single degree" doesn't seem to apply to the 42. that's all I'm saying, and I think it's true. This means I might be buying another grill from you soon..... Like maybe a 23 ultimate.