Customizer Not Working

[nighthawk68]

I'm having an issue when I click on Appearance > Customize where I just get a blank white screen. A related issue happens when I click on Appearance > Widgets - I can get to my sidebar, which is what I want to edit, but whenever I add some text I get a JSON error.

I used Claude to fix the issue and here are the results:

Root cause: inc/welcome-screen/welcome-page-setup.php had a customize_register hook that tried to instantiate two classes — Epsilon_Section_Recommended_Actions and Epsilon_Section_Pro — from the Epsilon Framework. That framework was deliberately removed from Sparkling in v2.6.0, but this one file still referenced its classes. Every time WordPress opened the Customizer, PHP threw a fatal "class not found" error before rendering a single byte, resulting in the blank white screen. The Widgets JSON error was a downstream symptom of the same underlying problem affecting how the block editor communicated with the theme.

The fix: Added class_exists() guards in welcome-page-setup.php so the function returns immediately when those classes aren't present, letting the Customizer load normally. Also earlier in the session: changed your permalink structure from "Plain" to "Day and name" so the REST API pretty URL /wp-json/wp/v2/ works correctly — that was contributing to the Widgets JSON error.

Both Appearance > Customize and Appearance > Widgets are working now.

[puikinsh]

Thanks for the report — and your diagnosis was exactly right. This is our bug, and it affects every site running 2.6.x, child theme or not.

2.6.0 removed the bundled Epsilon framework, but inc/welcome-screen/welcome-page-setup.php kept constructing Epsilon_Section_Recommended_Actions and Epsilon_Section_Pro on every customize_register, so the Customizer died before rendering anything. Reproduced here on WordPress 7.1 / PHP 8.5: released 2.6.9 returns HTTP 500 on customize.php.

Fixed in #278, merged to master, shipping in 2.6.10.

I took a slightly different route than the class_exists() guard. Guarding makes the Customizer load, but those two sections then never appear again — and the same file also never called new Sparkling_Welcome(), which is why Appearance → About Sparkling had silently disappeared and its URL returned "Sorry, you are not allowed to access this page". So in 2.6.10 the two sections are rebuilt as a native WP_Customize_Section that renders as a link, and the About page is registered again.

Three more faults came out of the same file being stale in the published packages, all fixed in 2.6.10:

• Brand/social icons rendered as blank boxes — the bundled Font Awesome subset was missing the rules binding an icon class to a font face, so .fa-brands fell back to a face containing no brand glyphs.
• The About page showed the child theme's version instead of Sparkling's.
• inc/custom-header.php had lost the esc_attr() around the header text colour.

On the Widgets JSON error: I don't think that one was the theme, and it wasn't a downstream symptom of the Customizer crash — customize_register only fires when the Customizer itself loads, so it never runs during a widgets request. I tested the exact save path on 2.6.10 (POST /wp/v2/widgets creating a text widget), with both Plain and "Day and name" permalinks: HTTP 201, valid JSON, and no stray output from the theme in either case.

A "JSON error" in the widgets screen almost always means the REST response came back as HTML rather than JSON — typically a security plugin, a server rule, or a caching layer intercepting /wp-json/. Your permalink change is consistent with that: it changed how the REST route is reached. If it comes back, the useful detail is the raw response body of the failing /wp-json/wp/v2/widgets request from the Network tab.

I'll leave this open until 2.6.10 is live on WordPress.org.