Directory not replaced with site name?
I just found and fixed the same problem. There are two possible fixes to this problem, only one of which is available to you immediately.  As per usual, Chris nails it.

In your civicrm.settings.php file, there's a line $civicrm_root = /path/to/civicrm.  If you have a symlink in that path, then the [civicrm.root] is miscalculated.  So the easy fix is to fix your $civicrm_root to the non-symlink path to the file.

The longer-term fix is this line:
CRM/Core/Resources.php:          'wysisygScriptLocation' =&gt; Civi::paths()-&gt;getUrl("[civicrm.root]/js/wysiwyg/crm.ckeditor.js"),

This shouldn't call civicrm.root, it should use the resource URL.  I'll try and post a bug report (and maybe even a fix!) if I find a moment - but first, like you, I need to get my mailing out :)