BuddyPress.org

You’re right that avatars on subdirectory blogs are acting a bit funky. It might be a BP bug, I have to look into it a little more. In the meantime, the following strategy might be a workaround for you. In your bp-custom.php, put a function like the following:

function bbg_avatar_paths( ) {
$root_url = get_blog_option( BP_ROOT_BLOG, 'home' );
define( BP_AVATAR_UPLOAD_PATH, ABSPATH . '/wp-content/uploads' );
define( BP_AVATAR_URL, $root_url . '/wp-content/uploads/' );
}
add_action( 'bp_loaded', 'bbg_avatar_paths', 7 );