content-toggle-block Suddenly Stopped Working on Backend

Problem Summary

• I use the Ultimate Blocks plugin with the Twenty Twenty‑Three theme.
• The Content Toggle block (ub/content-toggle-block) suddenly stopped working in the editor.
• In edit mode, WordPress shows: “Your site doesn’t include support of the ub/content-toggle-block. You can leave it as‑is, convert to custom HTML, or remove it.”
• On the front‑end, the block still renders correctly (tested in incognito).
• The issue is isolated to the block editor backend.

Steps Already Taken

1. Plugin reactivation: Deactivated and reactivated Ultimate Blocks.
2. Plugin reinstall: Uninstalled and reinstalled the plugin.
3. Block settings check: Verified Content Toggle is enabled in Ultimate Blocks settings.
4. SEO plugin disabled: Deactivated the only plugin that updated recently (SEO plugin). No change.
5. Rollback: Downgraded Ultimate Blocks to the previous version. Still broken.
6. Console check:

• Front‑end: no errors.
• Editor: multiple errors including:
  • Cannot read properties of undefined (reading 'ReactCurrentOwner') in blocks.build.js, link-attributes.js, single.js.
  • Store "core/abilities" is already registered.
  • Failed to load resource //stats.wp.com/w.js?67.
  • 403 error on /wp-json/wp/v2/block-directory/search?_locale=user.

Current Behavior

• Front‑end: Content Toggle works normally.
• Editor: Block is missing from inserter, existing blocks show “unsupported,” and console throws React errors.
• No recent changes: Aside from the SEO plugin update, no WordPress core or Ultimate Blocks update was applied manually. The issue appeared overnight.

Key Detail

The error stack (ReactCurrentOwner undefined) suggests a React/Gutenberg compatibility mismatch in the editor. The plugin’s compiled block scripts (blocks.build.js) are failing to mount against the current Gutenberg React runtime, even though front‑end rendering is unaffected.