I duplicated a working laravel app and renamed it to use for another app. I deleted the vendor folder and run the following commands again:
composer self-up
I also had a similar case after copying a project on a production server. The public folder was accessed by Apache via a symbolic link.
For Apache or the PHP service, the path to the project has not changed, thus they used cached file paths that lead to the old project repository.
Restarting Apache and PHP service resolved the issue.