I have this issue on chrome using Dawn theme
Topic summary
Users are experiencing issues with Shopify’s theme editor failing to load when clicking the customize button. The admin page loads normally, but the theme editor either loads extremely slowly or not at all.
Initial Troubleshooting Steps:
- Clear browser cache and use supported browsers
- Try Chrome Incognito mode or different devices
- Reset internet connection
- Test with other themes (like Debut) to isolate the issue
Identified Causes & Solutions:
- Shopify outage: A brief platform-wide interruption occurred on June 18, 2021, which was quickly resolved
- Third-party themes: Issues specific to certain themes (like Lorenza, WareHouse, Pipeline 2.0) may require contacting theme developers directly
- Custom code conflicts: Removing custom blocks from schema without first deleting them in the customizer causes loading failures. Solution: restore the code, remove blocks via editor, then delete code
- settings_data.json errors: Corrupted JSON files can prevent loading; editing and validating this file may resolve issues
- Browser extensions/antivirus: Disabling browser extensions or antivirus software has resolved the problem for some users
- Browser-specific: Some report it works in Microsoft Edge but not Chrome
Current Status:
The issue remains ongoing for multiple users across different years (2021-2023+), suggesting various root causes rather than a single platform-wide problem. Testing with default themes helps determine if the issue is theme-specific or system-wide.