Please use the following to restrict and redirect to group home page

/**
 * Restrict single group posts on the main blog.
 */
function buddydev_bcg_single_post_protect() {
	if ( ! is_singular() ) {
		return;
	}
	$post_id  = get_queried_object_id();
	$group_id = get_post_meta( $post_id, '_bcg_group_id', true );
	if ( ! $group_id ) {
		return;// not a group post.
	}

	$group = groups_get_group( $group_id );
	if ( ! $group->id ) {
		return;// the group was perhaps deleted.
	}

	if ( ! is_user_logged_in() || ! groups_is_user_member( get_current_user_id(), $group_id ) ) {
		bp_core_redirect( bp_get_group_permalink( $group ) );
	}
}

add_action( 'bp_template_redirect', 'buddydev_bcg_single_post_protect' );

Regards
Brajesh

Hi Hugo,
Thank you for posting.

We are using wp_login_url() so any plugin filtering on that url should do it automatically.

Here is the filter if the plugin is not doing it

/**
 * Filter login url.
 *
 * @param string $login_url login url.
 * @param string $redirect where to redirect.
 * @param bool   $force_reauth force reauth.
 *
 * @return string
 */
function buddydev_custom_sso_login_url( $login_url, $redirect, $force_reauth ) {
	return site_url( '/?auth=sso' );
}

add_filter( 'login_url', 'buddydev_custom_sso_login_url', 10, 3 );

You can put it in bp-custom.php or child theme’s functions.php and It will work.

Regards
Brajesh

Hi Carsten,
marking it resolved.
For others looking at it, It was an issue with one of the plugins causing lazy loading of image.

Regards
Brajesh

Hi Propertytips,
Is the blog post only visible in group page or is it part of your main site too? If it is part of the group page only, It can be easily achieved.

Please let me know and I will help.

Thank you
Brajesh