Replies: 1
If you site is old you maybe someday would like to change thumbnails sizes, as I am. For example, in my case my old size was 275×165, my new one is 350×210. If I update thumbnail via plugin it delete image-275×165.png and create image-350×210.png but do nothing with _wp_attachment_metadata, so gallery shortcodes and all thumbnail functions in template try to show deleted images with 404 errors, not new one with 200 server respond.
(I do not have this error with previous version of plugin.)