Why won't my theme editor load on the admin page?

Store Design

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.

Summarized with AI on November 2. AI used: claude-sonnet-4-5-20250929.
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i am still facing this issue right now and replied on 3 threads:

The Theme you’re looking for couldn’t be found

Check the web address and try again, or try navigating to the Theme Editor from Theme. and my theme is arena commerce: https://support.arenacommerce.com/support/tickets/263394 and I faced an error: and I am working on Firefox because am unable to work on normal browsing of Google Chrome i have an issue and reported CHROME SUPPORT and Shopify as well and hope soon it will be fixed but right now I am still facing this on firefox: https://prnt.sc/K9ExdYryXE6j any advice please would be much appreciated! this is really frustrating and so sad because I’ve been accessing the customer regularly and on a daily basis because this is my daily job work here and suddenly it stopped. i dont know what suddenly happened. can i create a new theme.liquid file from the other website? is this going to fix the problem now?

but how come from the same browser I can open theme editor for KADOONPRO here: https://www.kadoonpro.com/ but not the case for KADOON PRO UAE: https://kadoonpro.ae/. I was working normally on it today morning and all the time before. What’s happening here? I’m not sure if this is a Shopify issue because all other themes i have even the free one and demo i am able to customize easily. only the newsletter and the live theme ZEECO.

I cleared my cache and tried from Firefox and Chrome private browsing and facing this now: https://prnt.sc/TyTHVNOExE_n