When you have a BOGO discount in cart (1 + 1), then you use /cart/chage.js to update the line item properties of one of the product, it will update two product’s line item properties.
Loom: Screen Recording 2025-03-15 at 33852 PM | Loom
The video use line index as input, but it’s the same situation using line item key.
Could you please share your store URL so I can check and assist you better?
Here is the URL: https://hilaine.com/
Thank you for sharing store url.
Yes, this happens because Shopify treats BOGO (Buy One, Get One) discounts as a single unit in the cart. When a BOGO discount is applied, the cart groups the discounted product with the original product, making them dependent on each other.
You can try separating variants or, if you’re on Shopify Plus, use Shopify Scripts or Functions to customize the behavior.