Hello,
Got a lot of confusion when always no matter the permissions PS returned the following error.
Finally found the problem here:
src\Core\Domain\ImageSettings\CommandHandler\RegenerateThumbnailsHandler.php
Line: 99
$errors can return lot of other errors like original image missing (MY CASE) etc... But as we can see from the code it is not handled.
It's handling timeout, but everything else is thrown as Permissions error.
PS Version: 9.0.0