Thanks for every one!
This issue seems to disappear after the change in config. Our site is more stable than ever before in the last week with a rather short response time during the whole week.
Trying to login that way just bounced up my 'ne1up' Twitter real quick, then redirected back here to a 404 page. So I had to register...which was super easy and why I love this forum so much.
Yikes! That sounds like a serious issue. We'll get right on that...
@psychobunny, some relation to the Github SSO plugin you worked on?
Maybe interesting to do that to users 1 out've every 4 or so times, bounce them to an oops-404/register page.