There is probably a quick and easy answer to this. But I am preparing to be extravagantly outraged 
if there isn't and need your guidance!
I managed to book a Tesco slot at midnight last night, and just put a few things in the basket to check out and keep it reserved. I'm always up at the 80 items limit because we live rurally, can't get slots often, and need to shop for an elderly relative as well as our family.
So imagine my surprise when I saw that a shopping list that I would count as seven items was counted by Tesco as 21!
Are they counting individual items of fruit in a pack separately? How far does this go? What will happen if I buy a bag of peas? Or is it only if the number is in the description - so I'd be ok with a bag of 400 peanuts counting as one item but not a six-pack of beer?
Perhaps this is a Known Issue and I've just been happily oblivious until now - or a glitch of some sort?