[fmercalli]

I temporarily remedied with this hack:

function reset_bp_activity_oldestpage() {
    if ( ! wp_doing_ajax() )
        setcookie('bp-activity-oldestpage', '1', -1, '/');
}
add_action( 'wp_loaded', 'reset_bp_activity_oldestpage' );

[fmercalli]

Same issue here: bp-activity-oldestpage does not get reset when I reload a page with an activity-loop.php inside it.
After reloading the page afresh, when I press “Load More” I do not get page 2, but the last page visited before refresh + 1.