2 important issues

– Automatic redirect after upload via anchors # on list of upload files. Now is only echo File Upload Complete above form – this is confused for users.
– Subfolders must be in date format. Now is /wp-content/uploads/simple-file-list/file.pdf but must be /wp-content/uploads/simple-file-list/2018/09/13/file.pdf because if not this may be problem in cause of thousand files – it will be slowly FTP etc