Visual Editor gone

My visual editor is missing in a project

I’ve tryed the the following guide: https://ww.wp.xz.cn/support/topic/how-to-troubleshoot-visual-editor-issues?replies=3&view=all which includes deactivating ALL plugins, changing the theme, empting the cache and still at that point there was no Visual Editor, only the plain HTML editor.

Turning on define('SCRIPT_DEBUG', true); in the wp-config.php didn’t returned any error / warning in the browser console.

The editor’s tabs shows empty:
<div class="wp-editor-tabs"></div>
With the browser’s element inspector, I manually added the missing HTML tab code:

<a id="content-html" class="wp-switch-editor switch-html" onclick="switchEditors.switchto(this);">Text</a>
<a id="content-tmce" class="wp-switch-editor switch-tmce" onclick="switchEditors.switchto(this);">Visual</a>

Obvioulsly te tabs apeard but clicking on them returned the following JS error:
Uncaught ReferenceError: switchEditors is not defined onlick

I’ve also reinstalled WP (3.9.1) at:
/wp-admin/update-core.php

Still missing the Visual Editor… I’m getting desperate and my client isn’t happy. What I didn’t do was manually delete wp-admin, wp-include and re-upload from fresh WP installation but it’s a live site with heavy traffic and I’m not sure if this is safe.

One error that I’ve noticed when I turned debug on for a quick check was:

Notice: wp_enqueue_script and wp_enqueue_style was called incorrectly. Scripts and styles should not be registered or enquened until the wp_enquene_scripts, admin_enquene_scripts, or login_enquene_scripts hooks.

But how can I know which script caused that?