Had this identical scenario, was pulling my hair out, because it happened to me no matter what machine I tried from. I could log into anything VRChat related, the website, the SDK from within Unity, everything, EXCEPT VRChat itself.
Finally dropped VRC tech support an email detailing the issue, and my logs, and just as I thought, the issue was indeed on their end, not mine. They did one thing, and told me to try again, and bam, I got right on.