[Oxibug]

Hey Guyes,

This issue because you are using this function [bbp_list_forums] in [loop-single-forum.php] with old (2.5.0) default args array in your active theme.

You must use [bbp_get_forum_id()] in function’s args, So try to find this function inside the active theme and change the value of the [forum_id] argument.

bbp_list_forums( array(
    'before'            => '<ul class="bbp-forums-list">',
    'after'             => '</ul>',
    'link_before'       => '<li class="bbp-forum">',
    'link_after'        => '</li>',
    'count_before'      => ' (',
    'count_after'       => ')',
    'count_sep'         => ', ',
    'sep'               => '',
    'forum_id'          => bbp_get_forum_id(), /* Fix for bbPv2.6.3 */
    'show_topic_count'  => true,
    'show_reply_count'  => true 
) );

Hope it helps.