Block editor crashes when adding blocks with Jetpack active

Dear Jetpack support,

I’m experiencing repeatable block editor crashes on multiple WordPress sites when Jetpack is active, and I’m hoping you can help before I’m forced to remove Jetpack from all of them.

All the sites use custom, bespoke classic themes (not marketplace or block themes), but they work fine with the block editor when Jetpack is disabled.

With Jetpack enabled, the editor behaves like this:

• On a brand‑new post, the first default Paragraph block works.
• As soon as I add a second block, the editor crashes (“The editor has encountered an unexpected error”), and I can’t continue editing.
• This happens on multiple sites, not just one.

When I fully deactivate Jetpack, the block editor works normally and I can add multiple blocks; re‑enabling Jetpack immediately brings the problem back.

Because your support form doesn’t allow file attachments, I’ve pasted key debug information below.Environment (from Site Health → Info)

wp-core

• WordPress version: 5.9.10
• Site language: en_GB
• Environment type: production

wp-server

• Server: LiteSpeed on Linux
• PHP version: 7.4.33 (64‑bit)
• PHP SAPI: litespeed
• PHP time limit: 1200
• PHP memory limit: 1024M

wp-active-theme

• Theme: EM2020 (custom classic theme)
• Version: 1.0.0
• Theme features: core-block-patterns, widgets-block-editor, editor-styles, post-thumbnails, menus, html5, custom-background, custom-logo, custom-header, etc.

wp-plugins-active

(abridged list)

• Jetpack: 11.4.2
• Google Analytics for WordPress by MonsterInsights: 10.2.2 (now deactivated during testing, but was previously active)
• PHP Everywhere: 3.0.0
• Yoast SEO: 19.13
• All-In-One Security (AIOS): 5.4.9
• jQuery Updater, SVG Support, Simple Custom Post Order, Media Library Organizer, ProfilePress, WPIDE, etc.

jetpack

• Jetpack version: 11.4.2
• Plan: free
• Site ID: 138653830
• Jetpack plugin dir: /wp-content/plugins/jetpack/

I rely on Jetpack’s Custom Content Types (Testimonials and Portfolio), so I cannot simply remove Jetpack; those post types are in production use.Browser console (excerpt)

With Jetpack active, when I open the editor and add a second block, the console shows:

text

JQMIGRATE: Migrate is installed, version 3.3.2 admin-bar-v2.js?ver=11.4.2-202625:1 Missing data from PHP (wpNotesArgs).

Followed by many core block validation errors such as:

text

Block validation: Expected attribute class of value wp-block-button__link, saw wp-block-button__link wp-element-button. Block validation: Block validation failed for core/button. Content generated by save function: <div class="wp-block-button is-style-fill"> <a class="wp-block-button__link">Learn more</a> </div> Content retrieved from post body: <div class="wp-block-button is-style-fill"> <a class="wp-block-button__link wp-element-button">Learn more</a> </div>

Similar validation errors appear for:

• core/cover (background/gradient class differences),
• core/media-text (expected figure, saw div, different content order),
• core/quote, core/separator, and core/list (extra style attributes, empty list items, etc.).

At the end, I get a React error:

text

react-dom.min.js: Error: Minified React error #301; visit https://reactjs.org/docs/error-decoder.html?invariant=301 at Le (...) at Pj (...) at di (...) ...

On another site with the same behaviour, I additionally see:

text

default.editor.min.js?ver=20260616:1 TypeError: Cannot read properties of undefined (reading 'jsx')

where default.editor.min.js is loaded from the WordPress.com editor integration (wpcom-block-editor). With Jetpack disabled, this script is not loaded and the editor works.PHP debug log (excerpt)

debug.log contains only repeated Imagick warnings, and no PHP fatal errors at the time of the editor crash:

text

[16-Jun-2026 10:26:27 UTC] E_WARNING: Version warning: Imagick was compiled against ImageMagick version 1692 but version 1693 is loaded. Imagick will run but may behave surprisingly in Unknown on line 0

(Repeated several times.)Summary

From my perspective:

• On this stack (WordPress 5.9.10 + Jetpack 11.4.2 + PHP 7.4.33 + custom classic theme), enabling Jetpack causes the block editor to crash when adding a second block, even on new posts.
• The console shows Jetpack’s admin-bar script warning, core block validation mismatches, and a final React error #301 (too many re‑renders).
• On at least one site, default.editor.min.js from Jetpack’s wpcom-block-editor bundle is also throwing a TypeError: Cannot read properties of undefined (reading 'jsx').

I’ve already:

• Disabled MonsterInsights (its Headline Analyzer editor JS was causing a separate jsx error, which is now gone).
• Confirmed that disabling Jetpack entirely restores the editor, but I then lose Testimonials and Portfolio.

Questions

1. Is this a known compatibility issue between Jetpack’s wpcom-block-editor integration and WordPress 5.9.10 / PHP 7.4 / classic themes?
2. Is there a way to disable only the WordPress.com editor integration (e.g. the script that loads default.editor.min.js) while keeping Jetpack’s Custom Content Types for Testimonials/Portfolio active?
3. If this is a version mismatch issue, what combination of WordPress, Jetpack, and PHP do you recommend for a stable block editor when using Jetpack’s custom content types and a classic theme?

Because I can’t attach files via this form, I’ve pasted the key excerpts above, but I can provide the full debug.log, Site Health “Info” export, and complete console logs by email if needed.

Thank you in advance for your help—I’d very much like to keep using Jetpack, but right now the editor is unusable on all affected sites when Jetpack is active.

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