If you have a SSL cert that is from Symantec, Thawte, GeoTrust or RapidSSL that was issued before June1, 2016 you will need to get them replaced. Google announced some time ago that certificates from these vendors before this date will no longer be trusted. The new certificates should be offered to you by your vendor free of charge. Some time lines to be aware of:
March 2018 – Google is starting to push out Chrome 66 which will distrust the certificate by the above providers, if the certificate was issued before june 1, 2016.
September 2018 – Google is slated to start releasing Chrome 70 which will distrust the certificate by the above providers issued AFTER June 1, 2016 and BEFORE December 1, 2017.