Customizer Not Working

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.

Start in inc/welcome-screen/welcome-page-setup.php and inspect the customize_register hook and its references to the Epsilon classes. Reproduce Appearance > Customize and Appearance > Widgets, then verify both load without the blank screen or JSON error after the stale references are handled.