This article provides the explanation about the 1 year validity of the SSL Certificate and current Sectigo Policy for the certificates.
From Aug-Sep 2020, Google and Mozilla (together with Apple, who did it first) will no longer accept freshly issued certificates having a validity term of more than 398 days.
All publicly trusted SSL server certificates with a longer validity period issued before September 1, 2020 will be maintained for the whole duration.
If you have ordered a SSL Certificate after this period for 2 years, Sectigo will grant initially the certificate for 1 year (365 days) and at the end of 1 year period another year will be added automatically to your certificate via an automated reissue for which validation is required.
You can find more information in this article.