WordPress Media Uploader not displaying image that has just been uploaded

Your issue sounds like a visual bug in the WordPress Media Uploader’s interface after an image has been uploaded, especially since you mentioned that the image appears in the right-hand preview pane but not as a selectable thumbnail.

Try to force refresh the media frame after upload. You can use the add:attachment event to force the media frame to refresh when a new attachment is added. Add this right after you define your image_uploader object:

wp.media.model.Attachments.all.on('add', function(){
   image_uploader.uploader.uploader.refresh(); 
});

I haven’t tested this code, so just adjust it so it fits your code.

error code: 523