SHA2 certifcate not supporting in mobile

Perhaps the intermediate (or chain) certificate does not match the new certificate. When the CA issued the sha2 certificate, did they specify a intermediate certificate that is different from the one in the SSL client profile?

Internet Explorer will usually not give a certificate error in this condition (I think because Windows Updates load all of the major CA intermediate certs). But Firefox and Chrome, etc will give certificate errors. Just a thought.

Try checking your site in https://www.ssllabs.com/ssltest/index.html.