From https://bbpress.trac.wordpress.org/ticket/2151 ,here’s a quick hack to turn bbPress activity recording on, on sites that have the Discourage search engines option checked. Put this somewhere in functions.php or in your own plugin’s code:
<?php
add_filter( 'bbp_is_site_public', 'yourownprefix_enable_bbp_activity', 10, 2);
function yourownprefix_enable_bbp_activity( $public, $site_id ) {
return true;
}
?>
I was having the exact same problem, and yes un-checking Discourage search engines from indexing this site, does make bbPress activity start being recorded.
As to why this is so and if the behaviour is intended, your guess is as good as mine. If it *is* intended, I am extremely curious to know the twisted logic that dictated this implementation.