After Comodo rebranded into "Sectigo" on the 1st of November 2018. Since 14.01.19 major part of Comodo products will change root certificates. Products active since 14.01.19 will use new root during issuance and reissuance. Products been active before 14.01.18 are using old "Comodo" root for issuance and will use it for reissuance.
Since most browsers widely support the Addtrust External CA root certificate, the CA Sectigo continues offering this root certificate. At the time of the expiration of its relevance, customers already have Comodo RSA Certification authority root represented in the trusted root certificates, and it will be used automatically. As a result, installing the old root will not lead to problems until May 30, 2020. As far as we know, new customers are familiar with the Comoro RSA Ceritification authority root, and are already using it.
Currently certificates are issued for a maximum of two years.
As a result, the certificate may have a longer validity period than the root itself that you use.
This is due to the fact that the 'cross-signing' technique does causing no problems.
Some customers use legacy devices. They are recommend to the an old chain.
Since May 30, 2020 legacy devices that do not have a new root certificate in the list of 'trusted' will show an error.
If you faced with a problem of detection HTTPS as non-trusted on legacy Android device you should additionally install one more intermediate. Installation guides could be found here. Please find additional intermediate here.