Try using Google Publisher Console to debug the DFP ads, if need be.
Append ?...

Try using Google Publisher Console to debug the DFP ads, if need be.

Append ?google_console to your page's URL.

For example, if your page is located at www.drupal.com/page, you’d modify the URL to www.drupal.com/page?google_console.

Use the keyboard shortcut Ctrl+F10 (on a Mac, use Function+Ctrl+F10) to open the console

https://support.google.com/dfp_sb/answer/181070?hl=en