Support a non-standard media path

After changing the media date you copy it to a year/month folder (when the uploads_use_yearmonth_folders option is set). But you assume that the file is in the standard oldyear/oldmonth folder, and it’s not always the case when using a plugin which allows custom folders, for example “Media Library Plus”.

What I would suggest is checking if the file exists in the standard directory before trying to copy it.

...
		$metaolddata = array();
		$metaolddata = wp_get_attachment_metadata( $key );
		$new_file = $subdir.'/'.wp_basename($metaolddata['file']);
		$filename = wp_basename($new_file);
		$upload_old_path = $upload_dir['basedir'].$subdir_post;
		$copy_file_org = $upload_old_path.'/'.$filename;
		if ( $new_subdir && file_exists($copy_file_org) ) {
...

https://www.ads-software.com/plugins/post-date-time-change/