Recently, the main logo at the top of any wiki page disappeared, except for the one at the top of the "Special: Create Account" page. Unfortunately, this is hosted on a company intranet and I cannot share the site URL with you. Can anyone suggest why this may be happening (could the Create Account page and the other pages be using a different template, or something like that...)?
Topic on Project:Support desk
Try using browser developer tools (F12), maybe its Console tab logs an error on attempting to access the logo.
Custom styles (see Manual:Interface/Stylesheets) are not loaded by default on some restricted pages like the login or create account page (see Manual:$wgAllowSiteCSSOnRestrictedPages to disable that behavior).
Maybe you have something in MediaWiki:Common.css or similar which hides the logo, and because that style is not being loaded in the Create Account page that's why it's working there.