Invalid Root Certificate (Comodo RSA) Regularly, a duplicate certificate of COMODO RSA appears on my keychain (Google Chrome?) and when I browse on a website which use a COMODO certificate. Google Chrome blocks the website. (Normal). I muse delete it and restart Google Chrome to be able to open the website.

How is it possible to have this kind of duplicate certificate?

EDIT: A website using a Comodo RSA Certificate: https://www.graylog.org/
The COMODO RSA Certification Authority certificate (Serial Number 4C AA F9 CA DB 63 6F E0 1F F7 4E D8 5B 03 86 9D) is not a default trusted root in El Capitan. You can find the list of the trusted root certificates in El Capitan at https://support.apple.com/en-us/HT205204

That root became trusted in Sierra and later. You can find that list of the https://support.apple.com/en-us/HT205204. 

Either upgrade your macOS, or install the updated COMODO SHA-2 roots and intermediates from  https://support.comodo.com/index.php?/Knowledgebase/List/Index/71 and install them as X509 roots in Keychain.

Start with https://support.comodo.com/index.php?/Knowledgebase/Article/View/969/108/root-comodo-rsa-certification-authority-sha-2

Download the .crt file, click on it, and follow the instructions at https://www.askdavetaylor.com/how_to_install_trusted_root_certificate_mac/

Alternatively, you can use Firefox, which maintains a certificate store independent of the one in your outdated Keychain.