I have several websites which use Secure TLS services from Comodo the Validity dates are 3/16/2016 to 3/23/2017. We recently updated our certificates in March (as you can see) and prior to this tested my sites in China in January with no problems. Last week I noticed all sites reported a validation returns error [The exact report states “SSL Certificate Error Alert”].
I tested again and again clearing cache with the same result over 4G and over numerous wifi networks. Upon my return to Hong Kong I see no problem over wifi or 4G. Upon my return now to the UK I see no problems here either. Can you confirm that access to your validation server is being blocked.
For what its worth, I now notice Google Maps in blocked from within China, Google’s Playstore, all Drive Services (but allows folder reporting) and Gmail which again was not the case when I tested in January. Of course google.com has been blocked for several years now!