"Since we removed a reviews app, Add to cart does nothing on some products"

The most common Shopify theme bug after an app is uninstalled. Shopify removes the app, but the code it pasted into your theme stays behind. That leftover breaks the product page's script, so picking a size and pressing Add to cart silently fails. Switch between the broken store and the fixed one and try it.

The product page broken

yourstore.com/products/linen-shirt

Linen shirt

$48.00
Liquid error (sections/main-product line 212): Could not find asset snippets/reviews-widget.liquid

What the browser and the theme code say

Pick a size and press "Add to cart".

How it gets fixed without risking the live store

  1. Duplicate the live theme (Online Store > Themes > Duplicate) and work only on the copy. The store keeps selling the whole time, and switching back is one click.
  2. Find what the app left behind. The page itself shows Liquid error ... Could not find asset snippets/reviews-widget.liquid, and the console shows Uncaught ReferenceError: ReviewsWidget is not defined in the product script. A search of the theme code finds the leftover {% render 'reviews-widget' %} tag and the app's script include.
  3. Remove only the leftovers - nothing else in the theme changes.- done here: the render tag and the dead script include are gone from sections/main-product.liquid and layout/theme.liquid; the variant script now runs, so the size picked is the size added.
  4. Test on the copy with Preview: every product template, variant picker, quick-add, cart drawer and checkout button, on desktop and a phone.
  5. You publish the copy when it looks right, and keep the old theme as a one-click backup. You get a note listing each file and line that changed.