This is Luna from Shopify. I noticed you are new to our Community forum, welcome! Sorry to hear you've been dealing with this setback. I'm happy to help out.
To gather a little bit more context, what browser are you using? Is this happening on several devices? I recommend ensuring that you are using one of our support browsers. From there, you should clear your browser cache. After this, please try to close the browser completely and restart it before using your theme editor once again.
If that doesn't resolve the issue, please also try the following:
In the meantime, if this persists further I will ask that you try to customize another theme in your admin. Does the same error occur? To do so, please follow these steps:
If you don't currently have any other themes downloaded, please download a free theme for testing purposes. To do so, head back into the 'Online store > Themes' section of your admin, click on 'Explore free themes', click on any free theme, and then click 'Add to theme library'. Once this theme has been downloaded, please follow the steps listed above. Once you are finished, feel free to delete the theme from your library.
I'm looking forward to hearing how this goes for you. I appreciate your patience while we work to get this sorted out together.
Luna here. Were you able to resolve the error with those suggestions? If you are still facing any setbacks, please don't hesitate to let me know. We can continue to look into it together.
Thanks for getting back to me and completing the troubleshooting steps I provided above. I appreciate it! Based on what you've shared, it sounds like the issue is isolated to your theme's current version.
To gather a little bit more context, can you please let me know the following:
My understanding is that you've made some modifications to your theme's coding, is that right? If so, our next best step will be to find the route of this error based on the customizations that have been made. Please take a look at our help document: Troubleshooting.
As an alternative to reverting to an older theme, rolling back your current theme may be a better solution to resolve the issue. If you haven't made any customizations to the theme or recently downloaded any apps, please let me know.
Looking forward to hearing back from you, so that we can continue to work on this together.
Just checking in with you. Were you able to resolve this? If you have any questions or require additional assistance don't hesitate to reach back out.