theme_debug doesn't work
People have been facing issues with Theme Developer module. If you installed this module just to get template suggestions, you might want to uninstall it and use theme_debug (only for d7) variable instead.

Enable this variable by adding $conf[theme_debug] to your settings.php or drush vset theme_debug 1 

Then Perform a element inspect (or) view page source to get template suggestions. You may find this article on drupal and the answer in this post helpful- self promoting my answer.