SSO is Single sign on. So meaning you sign in with your google account vsan email (which could still be a gmail) with password.I think I went into security settings to change it.

I finally figured this out. I unlinked my Google SSO and set up a password.Seems like a bug and 2FA should work with sso, but this worked for me!

I'm experiencing the same issue as well. I've turned 2-step authentication off, tried an incognito browser, and tried Safari on my phone. Nothing has worked. This is incredibly frustrating. 

I'm stuck in this same loop as well and it's incredibly frustrating!!