Since air frying manages to use no oil or very little oil the oils in meat like chicken tend to be sucked up & deposited on the inside of the lid. You need to occasionally clean that oil off. It's not that easy since you can't soak the lid. I use Viva cloth type paper towels & manage to get the oil buildup off.
Experiment with setting the temp & time instead of the pre sets. French fries depending on quantity in the basket can take longer. For French fries my wife soaks the fries in ice water for a 1/2 hour. Dries them then slightly oils & lightly salts them. The fries come out crispy on the outside well cooked but tender on the inside just like you would get at a fast food place.