Using fictional domains here instead of the actual ones I have this situation:
domain1.com has binding set up in IIS and is linked to SSL and has "Require Server Name Indication" checked.
domain2.com has binding in IIS and is linked to it's own SSL and has "Require Server Name Indication" checked.
Going to https://domain1.com in a browser works fine.
Going to https://domain2.com in a browser gives an error : NET::ERR_CERT_COMMON_NAME_INVALID "This server couldn't prove that it's domain2.com; its security certificate is from domain1.com."
I can't undertsnad it becasue SNI is definitely checked for both and they are the only 2 https bindings for that IP. I have tried restarted the site in IIS and recycling the AppPool but that makes no difference.