I’m getting the same issue. I can access answerhub when logged out, but logging in redirects to https://answers.unrealengine.com/oauth/error.html. Navigating to another page on answerhub (my profile, index.html) gives the “Internal error has occurred” page.
I’ve tried clearing cookies, and also tried to visit the site from a browser in a VM that has never been used to access answerhub. Same results as above in both cases.