Why does the wrong product size keep getting added to the cart?

Shopify Discussion

Topic summary

Multiple Shopify store owners report a persistent bug where customers select a product size (e.g., XL), but the cart defaults to the smallest size option (typically Small) instead. This issue has been occurring for at least 2+ years across different stores.

Key characteristics:

  • Appears random: not tied to specific sizes, devices, or browsers
  • Always defaults to the first variant in the list
  • Affects only some items in multi-item carts
  • Reported across multiple themes (Venture, ICON 2.0, BOOST) and device types
  • Some users report it happens primarily on mobile devices (Samsung browser, Apple iPhone)

Attempted solutions (unsuccessful):

  • Multiple Shopify support escalations to senior staff
  • Deleting apps
  • Switching themes multiple times
  • Theme developer consultations

Current status:
No confirmed solution has been found. One user suspects Shopify’s “add first variant by default” setting may be involved, but this remains unverified. The issue continues to cause lost revenue and customer frustration, with at least one store owner considering migrating to another platform.

Summarized with AI on October 26. AI used: claude-sonnet-4-5-20250929.
5

I see lots of people seem to be having the issue of when a customer chooses a product size, after adding it to the cart, the size is defaulted back to the first size in the list. For example…if you choose a size XL, add it to your cart, go to cart, you will see that it now is back to Small, which is the first size variant in the list?

I have also asked Shopify, and the developer of the theme BOOST…anyone have any luck figuring this out?

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