If you disabled search engines from indexing your site (under “Settings > Reading” in the WP dashboard), then bbPress will not add any activity entries to the site. Or few hostings automatically disabled it for a reason we do not know. To fix it please use this snippet
add_filter( 'bbp_is_site_public', '__return_true' );<br>
Put it on "bp-custom.php" file in folder "wp-content/plugins". If you do not have the file yet, please create a new one.