If you have a itemstack saved in a config deserialized in 1.17 then update to 1.18 a value named "v" changes to "2860" whilst still being "2730" in the config will cause them to not equal eachother even though they are the same exact item.

Config for example

  itemstack:
    v: 2730 (1.18 itemstack are 2860)
    type: DIAMOND_SWORD
    meta:
      ==: ItemMeta
      meta-type: UNSPECIFIC
      Damage: 2 

player.getInventory().containsAtLeast(configitem, 1) //Will return false if one is a ItemStack from 1.17