Safari 13 on High Sierra Can't log in to Apple Sites

Just wanted to find out if anyone else is seeing this - I have multiple machines running the latest updated build of High Sierra and Safari 13, and none of them can log in to any Apple-owned websites.

Attempting to log in to https://itunesconnect.apple.com just loads an empty white page, with the web inspector showing errors establishing an SSL connection to idmsa.apple.com:

Trying to log in to these forums results in a similar problem:

A system that is still running Safari 12 seems to be able to load them ok.

Just wondering if anyone else could test this for me?

Thanks.