This scenario is presented when more than one item from the same SKU is splitted into more than one line in the cart. This occurs due to an action called apportionment - that is the division of a value among some items.

However, there are scenarios in which the discount amount is indivisible by the number of items, particularly in cases where the SKU has a multiplier unit. So, you need to give different discounts to items of the same SKU for the discount amount be correct. This ends up assigning different prices, and splitting each unit in a line.

The example below helps to understand this concept :

1. Multiplier unit.
2. Product price after discount.
3. Product price with the difference due to the apportionment.
4. Discount applied.