First site onmulti-site install disappeared since upgrade to 3.1.1

Might wanna double check those www DNS records.

Thank you for your reply. No, my DNS records are OK: when I replace the DocumentRoot for this virtual host on my Apache, so that it points to a static website, it works.

I can access the admin ages for the other sites on the same server (example: https://jmg.mantano.com/wp-admin). I cannot access the admin page for this https://www.mantano.com site (https://www.mantano.com/wp-admin/). From the admin pages of another website such as jmg.mantano.com, I cannot access the Network Settings, because its URL is: https://www.mantano.com/wp-admin/network/.
When trying to access https://jmg.mantano.com/wp-admin/network/, I’m redirected to https://www.mantano.com/wp-admin/network/…

I don’t know in which direction I should investigate…

Then go double check your htacess file, your wp-config file and the database.

Solved! I had to replace www.mantano.com by mantano.com in the wp_site database table. In my wp-config I have define( 'DOMAIN_CURRENT_SITE', 'mantano.com' );
Thanks for your help. Marking as “resolved”.