Private Subfolder and Public sub sub folder ?

You have a blog within a blog?

https://www.tld.com/blog1/blog2

That’s an odd one.

Subdirectory blogs should expect blogs to be
https://www.tld.com/ – (blog 1)
https://www.tld.com/blog2/
https://www.tld.com/blog3/
https://www.tld.com/blog4/

Anyway, disable my plugin and make certain you can access the blogs you expect at https://www.tld.com/blog1/blog2. My plugin should not interfere and redirect you to a different blog, WordPress is doing that. As for your SEO, subdir robots.txt may be irrelevant if the main domain robots.txt is in denial.

Hi thx for your response
As an example when you set up a blog (WPMU) your config.php file will include :

define(‘MULTISITE’, true);
define(‘SUBDOMAIN_INSTALL’, false);
define(‘DOMAIN_CURRENT_SITE’, ‘www.tld.com’);
define(‘PATH_CURRENT_SITE’, ‘/blog1/’);
define(‘SITE_ID_CURRENT_SITE’, 1);
define(‘BLOG_ID_CURRENT_SITE’, 1);

So I would like to connect with a password to tld.com/blog1
and without to tld.com/blog1/blog2

I don’t do anything with wp-config.php to use this plugin. If your multisite is making and access all blogs without the plugin it should add the extra privacy options just the same.

In my test install setup with
tld.com/blog1/
tld.com/blog1/blog2/
tld.com/blog1/blog3/
tld.com/blog1/blog4/
etc

I can set a password in reading settings @ tld.com/blog1/wp-admin/options-reading.php

I can access https://www.tld.com/blog1/blog2/ normally without redirecting as you report.

I can’t reproduce your error.

I have a couple differences in the wp-config.php that WP autogenerates for my case for you to compare:

/* Multisite */
define('WP_ALLOW_MULTISITE', true);
define('MULTISITE', true);
define('SUBDOMAIN_INSTALL', false);
define('DOMAIN_CURRENT_SITE', 'tld.com');
define('PATH_CURRENT_SITE', '/blog1/');
define('SITE_ID_CURRENT_SITE', 1);
define('BLOG_ID_CURRENT_SITE', 1);