Image field upload shows a broken preview until I reload the page When I upload an image it does an AJAX upload and then tries to show the thumbnail but the thumbnail style of that image is not available, so it shows up as a missing image. If I save and come back to the form, then it displays fine.
make sure the "image style" of your image field exists. for example to make sure about our "Article" content type, we check the path below:


  http://yoursite.com/admin/structure/types/manage/article/fields/field_image


find your "image style" name and then go the path below:


  http://yoursite.com/admin/config/media/image-styles


check the image styles name and make sure "Article" image style is here. if it's not, you have to change image style of your content type.