Hello,
The most common issue of that warning is using wrong file paths: https://laracasts.com/discuss/channels/laravel/after-upgrade-laravel-6-to-7-why-psr4-composer-warning or some error about how phpdocx has been to composer.json. Please note that we recommend adding phpdocx to classmap (https://getcomposer.org/doc/04-schema.md#classmap) in composer.json (https://www.phpdocx.com/documentation/cookbook/integrate-phpdocx-with-composer).
As you included support tickets with your license, we recommend you to open a support ticket on MY PHPDOCX page and attach the composer.json file you are using and also post in the same ticket the composer version and we'll check them.
Regards.