Thanks, I was able to reproduce the issue. It looks like the website is using
SNI (Server Name Identification) which requires the SSL client to use an API that specifies the server named address before connecting to the server, which mIRC does not support. I have added support for this in the next version. That said, I am not sure if there are any side-effects to setting this option. In testing, with this feature enabled, I have not yet experienced any issues when connecting to SSL servers, so it seems fine but we will need to see how it works out with greater use.