When the custom post type API option is set to TRUE then the author dropdown list only shows the admin users. However, when it is set to FALSE, all users show. I want all users to show. But unsure why this is happening. It is only on the edit post admin page, not the quick edit. I have disabled all my code and plugins, and this did not solve it.
I don't see that issue on my site. The list of users in the Quick edit is the same when editing the post. Please try to generate the PHP code and register the CPT by code then deactivate all plugins, switch to a standard theme of WordPress then check this issue again.