Extension hints not working when attempting to debug

[Feanor]

I'm using Visual Studio Code with the PHP Intelephense and PHP Debug (xdebug) extensions.

extension_hint.php seems to be working fine while coding. No errors.

However, when attempting to debug, I get this error:
PHP Fatal error: Uncaught Error: Class "[addon id]\Pub\Controller\XFCP_Thread" not found in [addon path]/Pub/Controller/Thread.php:10

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