Image preview thumbnail does not display Drupal 7.

When adding a core image field to a content type to display an image, the preview thumbnail does not display on the edit page when uploading an image.

What appears after clicking on the "Upload" button is a placeholder for the image and an image icon. The placeholder then quickly disappears to leave the icon and the name of the file. It looks like the link is broken and the image cannot be found. However, the uploaded image and it's preview (thumbnail image style) are in the right folders. This is confirmed when the edit page is reloaded (browser refresh or a new visit to the page) because the preview image then displays properly on the edit page..

Clicking the Save button displays the image in the content.

However, if I do not click the Upload button and click on the Save button directly instead after selecting an image with the Browse button, the content image is not displayed either unless I click on the browser Refresh (or go to another page and come back.)

A few people have had this issue. 

In this Youtube tutorial, the issue is reproduced (the thumbnail does not show up.) The instructor notices it but gives no solution: Drupal Tutorials #9 - Custom Content Types Part 2 Manage Display 

Does anyone know what's going on and how to fix this?

Any and all help will be greatly appreciated. :)
Try removing any space, empty line before 

https://www.drupal.org/node/2195311

Hope this helps.