Image field upload shows a broken preview until I reload the page
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.