Getting a 404 error when clicking edit page

You mentioned that you disabled all plugins, and changed the theme (I assume you used one of the ‘twenty’ themes, which is what I usually do when trying to find theme/plugin problems).

Did you also look at the ‘must use’ plugins (in wp-content/mu-plugins ) (see https://codex.wordpress.org/Must_Use_Plugins ). Maybe a plugin in there is causing problems.

I’d also look at the Network tab in Developer Tools (in your browser, usually F12) to see what request element is actually causing the 404. That might point you to the plugin/theme/whatever problem.

You could also do a re-update of WP (in the Admin, Updates) section to see if there is some missing core code.

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