Thanks for reporting that @anphonic! I've sent this information to our internal teams to see what we can do about this. Thanks again!
Hi @JakePrevatt, our team is still looking into this issue. Sorry for the delay on this.
From the investigation we did, we haven't discovered a case that wasn't either a temporary hiccup in GitHub's services or an improperly configured setting in the corporate proxies themselves. You might want to doublecheck the corporate proxy settings and if everything looks good there, contact GitHub Support directly so that we can help you troubleshoot on a case to case basis.