Hi Chris I had the same problem. I tracked the Ajax request that is send while uploading a new image. In the answer you might receive an error like so:
getimagesize(): https:// wrapper is disabled in the server configuration by allow_url_fopen=0 in /homepages/u56924/beta/wp-content/plugins/drag-drop-featured-image/index.php</b> on line 495
As you can see the problem is that my server (and I bet your server as well) by default disallows loading files, which the function getimagesize() does by using fopen().
So what you could do is upload a php.ini file to your server with the following content, for each folder starting from your wordpress main-folder to the plugin folder…
But as you might not need the image-size information I suggest editing the plugin index.php like this (line 493):
// Get image sizes and correct thumb:
$croppedImage = wp_get_attachment_image_src($attach_id, 'full');
//$imageDetails = getimagesize($croppedImage[0]);
// Create response array:
$uploadResponse = array(
'image' => $croppedImage[0],
//'width' => $imageDetails[0],
//'height' => $imageDetails[1],
'postID' => $post_id
);
Now the endless spinning problem is solved but as wordpress now uses responsive images the next problem is, that the srcset-attribute migh override the src-attribute, so you might get the old thumbnail if there is one. So you may want to add the following after line 421:
imageObject.removeAttr('sizes');
imageObject.removeAttr('srcset');
This is just a quick and dirty method as you disable the image being responsive but never mind. ??
Hope this helps to you as well.