A5hleyRich
commented
7 years ago GD supports stream wrappers, but Imagick doesn't. When a stream wrapper is detected and wp_get_image_editor returns an instance of WP_Image_Editor_Imagick we need to temporarily copy the full size file locally to perform the resize.
Currently, this doesn't work when the local file has been removed from the local server. Needs further investigation, but I'm not sure if GD or Imagick support stream wrappers. We may have to download the file locally resize it, then upload to S3 as a workaround.