Elementor 3.6.x, historical compatibility issues

Historical note: Elementor 3.6 is no longer a current version. Do not reinstall it to solve a current case; use maintained, compatible versions of Elementor, Elementor Pro, WordPress and PHP.

When it was released, 500 errors, freezes and save failures were seen after updating. Those symptoms do not necessarily share the same cause: reproduce the same action and check the first error in the PHP log or the browser console.

Elementor 3.6 included internal changes to classes such as Scheme_Typography and Scheme_Color. If the fatal error mentions one of their old paths inside an add-on, that entry does provide evidence that the add-on needs updating.

Current diagnosis

1. Make a backup and note the versions of WordPress, PHP, Elementor, Elementor Pro and their extensions.
2. Reproduce the failure once and record the time, URL and HTTP code.
3. For a 500 or a blank screen, check the PHP log. For a visual failure, check the browser's console and network views.
4. Update Elementor and Elementor Pro together according to the vendor's requirements.
5. If an extension appears in the error, repeat the action without it on staging and ask its developer for a compatible version.

If the page has only lost its styles and there is no PHP error, regenerate the files and data from Elementor > Editor > Tools (in older versions, Elementor > Tools) and clear the cache once. Then repeat exactly the action that was failing, check that no new entry appears in the log and also check a public page.

Do not install an old version downloaded from an unofficial site to get those classes back. If an extension still depends on them, ask for a compatible version or plan its replacement. Keep the historical reference of the error to locate the caller, but validate the solution with the versions you are actually going to maintain.