[r0z]

I solved this error without having to disable the SEO in BuddyPress pages, and without having to touch the core of the plugin.
I’ll leave here (add in functions.php):

function wpseo_fix_title_buddypress($title) {
    // Check if we are in a buddypress page 
    if (function_exists( 'buddypress') && buddypress()->displayed_user->id || buddypress()->current_component ) {
        $bp_title_parts = bp_modify_document_title_parts();

        // let's rebuild the title here
        $title = $bp_title_parts['title'] . ' ' . $title;
    }
    return $title;
}
add_filter( 'wpseo_title', 'wpseo_fix_title_buddypress');

maybe this code or something similar would need to be implemented in Yoast SEO plugin… maybe.