Full Image does not Open After Clicking on Thumbnail if the server base URL is not configure correctly. After clicking on the thumbnail, Confluence only shows a continuously spinning loading icon as shown below:

Steps to replicate

1. Set the server base URL via Administration Console >> Administration Console >> Site Configuration >> Server Base Url to incorrect URL. (eg: http://localhost:8080)
2. Now on the same machine upload a new image and use the following example macro shown below:

   !<image file>|thumbnail!
   

   NOTE: Please change the <image file> according to the image file name you have uploaded.

3. Now grab another machine try to click on the thumbnail.