I have a domain set up with SSL/TLS using a StartCom Class 2 certificate. When accessing it from a web browser (mobile or desktop: Firefox, Firefox Mobile for Android, iOS Safari, Chrome or IE11) there is no problem, but when accessing it from a Lumia 630 (WP 8.1) with the standard browser I get:
"Certificate error [...]" - "We're having trouble with this site's security certificate. It looks like the security certificate wasn't issued by a trusted certificate authority. This can indicate an attempt to fool you or access information that you send to the server."
The interesting thing is that other phones running WP (a Lumia 1520 running the exact same OS version, and a Lumia 920) can access the domain without getting certificate errors. I have tested the web server configuration with SSL Labs (Qualys) and it gives an overall A- rating, saying the certificate is trusted and there are no chain issues.
We have tried a factory reset (and then updating) but the problem remains.
The phone runs Windows Phone 8.1 OS version 8.10.12397.895