I found the culprit!
The file in questioned is “content-single-forum.php” in “bbpress”.
Removing the line below solves the problem.
<?php bbp_forum_subscription_link(); ?>
Step by step guide to setting up a bbPress forum – part 3
The usage of child theme is to avoid overwriting any customization that you have done to your site by a theme/plugin upgrades. So you maintain a separate set of files in different folder than the out of box themes or plugins. This way whenever there are new upgrades and get pushed and overwrite your files, it won’t overwrite whatever customization you had.
