Quick answer: When the storefront works but the theme editor fails, the problem is often design-mode code, invalid Liquid, malformed HTML, heavy loops, app embeds, or missing snippets. Duplicate the theme and isolate the failing template or recent change.
The real symptom
The live storefront loads, but Online Store → Themes → Customize shows a blank preview, failed-to-load message, HTML error, or Liquid memory-limit warning.
Likely causes
- Invalid Liquid in a section or snippet.
- Malformed HTML breaks the editor iframe.
- A nested loop exceeds Liquid limits.
- Code runs only when request.design_mode is true.
- An app injects editor-specific JavaScript.
- A template references a deleted section or snippet.
- A JSON template or section schema is malformed.
Confirmed Community fix
Community cases show errors such as Liquid memory limits exceeded even when the storefront works. Other cases are resolved by correcting the named Liquid file, restoring missing assets, or fixing malformed HTML.
Exact admin path
- Go to Online Store → Themes.
- Duplicate the affected theme.
- Try Customize on the duplicate.
- Read any displayed file and line number.
- Open Edit code.
- Inspect the named file and surrounding Liquid/HTML.
- Compare recent changes or older versions.
- Simplify or remove the newest change and retest.
Simple checks
{% if request.design_mode %}
{%- comment -%}
Inspect loops, app initialization, and data-heavy rendering here.
{%- endcomment -%}
{% endif %}If every template fails, inspect layout/theme.liquid, global sections, app embeds, and design-mode code.
Do not do this
Do not delete random live-theme sections. Duplicate the theme first and use the error’s file and line information.