Themify Builder error: Template not found: #tmpl-builder_subrow_item

<span style=”font-size: inherit;”>Hello,</span>

I have an issue with Themify Builder on some WordPress pages.

Environment:

• WordPress: 6.8.5
• PHP: 7.4.33
• Themify Builder version: 5.6.6

Problem: The frontend of the pages displays correctly, but I cannot open certain pages in Themify Builder editor. The builder keeps loading and throws this error in browser console:

<code dir="ltr">Uncaught Error: Template not found: #tmpl-builder_subrow_item

The error appears in:

• themify-builder-app.js
• themify-builder-visu.js
• themify-constructor.js

Important details:

• Only some pages are affected.
• Newly created pages may work normally.
• Frontend display is correct.
• The issue happens only in Builder editor/admin.
• I already disabled caching/optimization plugins and security plugins for testing.
• I tested with WP Rocket disabled.
• I also tested disabling plugins like Wordfence and review plugins, but the problem remains.

Could this be related to a corrupted subrow/nested row structure or compatibility issue with older Builder data?

Can you advise:

1. How to identify the problematic subrow/module?
2. Whether there is a way to repair builder data?
3. Whether Builder 5.6.6 is fully compatible with WordPress 6.8.5?

Thank you.