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SmartSize stopped working after a theme change

Guide type: Troubleshooting guide
Difficulty: Intermediate
Applies to: Storefront setup, custom themes

Use this guide when the SmartSize Size Chart or Find my size button was showing on your storefront, but disappeared after you switched to a new Shopify theme or updated your current theme.

Symptoms

You may see one of these symptoms:

  • the SmartSize button no longer appears on any product page
  • the button appears on some products but not others
  • the button is in a different position than before
  • the button appears in the theme editor preview but not on the live storefront
  • the popup opens but styling is broken or unreadable
  • the browser console shows JavaScript errors related to SmartSize

Quick checks

1. Check the App extensions status

From the SmartSize Home page, open the App extensions card.

Check whether the extension you need is Active on your live theme:

  • Size chart extension for size charts
  • Fit quiz extension for fit quizzes

If the status shows Inactive or mentions a different theme, the app embed was not carried over to your new theme.

2. Re-enable the app embed in the new theme

If the app embed is not active on your new theme, turn it on in the Shopify theme editor.

For step-by-step instructions, see Turn on the SmartSize app extensions.

3. Check that you saved the live theme

Changes made in a draft or development theme do not affect the live storefront.

Confirm that you saved the app embed settings in the theme your shoppers see.

4. Test button placement

Different themes have different product page structures. Automatic placement that worked in your old theme may not work in the new one.

Open a product page and check whether the button appears at all. If it does not, try a different placement method:

  • Floating button — works on almost any theme
  • App block placement — lets you place the button manually in the theme editor

For placement options, see Choose where the SmartSize button appears.

I switched to a standard Shopify theme

If you changed from one standard Shopify theme (such as Dawn, Refresh, or Craft) to another, the most common cause is that app embed settings are theme-specific and are not carried over automatically.

Cause: app embed not enabled on the new theme

What happens: Shopify app embeds are theme-specific. When you switch themes, the new theme does not inherit the old theme's embed settings.

Fix: Open the Shopify theme editor for your new live theme, go to App embeds, find SmartSize, and turn on the extension. Save the theme.

Cause: saved in a draft theme instead of live

What happens: You turned on the embed in a draft or development theme, but your shoppers still see the old live theme.

Fix: Publish the draft theme, or open the current live theme and enable the embed there.

Cause: the new theme structure breaks automatic placement

What happens: The app extension is active, but the new theme uses a product page layout that automatic placement cannot detect.

Fix: Switch to Floating button placement. This does not depend on the product form structure and works on most themes.

If you want the button inside the product details, use App block placement and add the SmartSize app block manually in the theme editor.

Cause: product display rules no longer match

What happens: The new theme uses different collections or product types, so the old product display rules no longer match.

Fix: Open the size chart or fit quiz, review the product display rules, and update the conditions to match the new theme's product structure.

I have a custom or heavily modified theme

If your theme is custom-built, heavily modified, or headless, the standard Shopify app embed infrastructure may not load SmartSize correctly even when the embed is turned on.

Cause: the theme does not support app embeds

What happens: Some fully custom or headless themes bypass the standard Shopify theme infrastructure. App embeds may not load at all.

Fix: Check with your theme developer whether the theme supports Shopify app embeds. If not, SmartSize may need a custom integration using the JavaScript API or a manually placed script.

For developer guidance, see SmartSize app embeds for custom themes.

Cause: CSS conflicts

What happens: Your theme's CSS overrides SmartSize popup styles, making the popup unreadable, misaligned, or hidden.

Fix: Ask your developer to inspect the SmartSize popup elements and adjust the theme CSS so it does not target SmartSize classes. SmartSize uses scoped CSS, but aggressive global theme rules can still interfere.

For CSS class references, see CSS customization reference.

Cause: JavaScript conflicts

What happens: The theme's JavaScript blocks or conflicts with SmartSize scripts, preventing the button or popup from working.

Fix: Ask your developer to check the browser console for errors and adjust script loading order so SmartSize scripts are not blocked.

Cause: automatic placement cannot find the product form

What happens: Custom themes often use non-standard HTML structures. SmartSize automatic placement looks for standard Shopify product form selectors and cannot find them.

Fix: Use Custom selector placement. Your developer can provide a CSS selector that points to the exact element where the button should appear.

For placement options, see Choose where the SmartSize button appears.

Cause: the theme uses app blocks instead of app embeds

What happens: Some custom themes support app blocks on specific templates but not app embeds globally.

Fix: Add the SmartSize app block manually to the product template in the theme editor. Place it where you want the button to appear.

Check the result

After applying a fix:

  1. Save all changes in Shopify and SmartSize.
  2. Open a product page on the live storefront.
  3. Refresh the page.
  4. Confirm that:
  5. the SmartSize button appears
  6. clicking the button opens the popup
  7. the popup looks correct and is readable
  8. the popup does not overlap important content
  9. Test on both desktop and mobile.

If it still does not work

Contact SmartSize support and include:

  • the name of your new theme or a link to the theme developer
  • the product URL where SmartSize is not working
  • a screenshot of the App extensions status card
  • a screenshot of the theme editor App embeds panel
  • a screenshot of the browser console showing any errors
  • a description of what your developer has already tried
  • whether the theme is headless, custom-built, or a modified standard theme

This helps support determine whether the issue requires a custom integration, a CSS adjustment, or a JavaScript fix.