fluctuations occur even during normal cooking.
Disregard anything to do with opening or peeking into the cooker....
Mine normally goes +10 / -10 of target creating almost a 20° difference. As long as it goes up and down and doesn't stay for an extended time period, I just let it go. If it goes for an extended time then I make a MINOR adjustment.
Humphrey's Down East Beast, Weber Kettle, Kenmore Elite Gasser, Camp Chef Smoker, Camp Chef Denali