Near the end of July 2017, Google Chrome created a plan to first reduce and then remove trust (by showing security warnings in the Chrome browser) of all Symantec, Thawte, GeoTrust, and RapidSSL-issued SSL/TLS certificates. Google broke this timeline up into 3 important dates. December 1, 2017, March 15, 2018, and September 13, 2018. The first date, December 1, 2017, required no action from you. However, for the 2018 dates, you must replace affected certificates to avoid Google Chrome browser security warnings.
DigiCert took over validation and issuance for all Symantec Website Security SSL/TLS certificates. This includes certificates for Symantec and its subsidiary CAs: Thawte, GeoTrust, and RapidSSL. Going forward, all new and reissued Website Security certificates are issued by DigiCert (using one of our trusted roots) and are trusted by Google Chrome
The new certificate chain DigiCert created does not interfere with your current certificate trust among browsers. The chain also establishes trust for your replacement certificate with Google Chrome (and other browsers) going forward.