It's down for me as well. Login with my ID gets me general error, ID not available etc.
This is regardless of browser or cleaned cookies, AND it happens in the App as well (login, no-bot verification, login, no-bot etc. - i.e. a loop).
I assume some issue with their DB affecting some accounts only or their authentication. FYI, I am using an LH ID - not M&M (as I am a Mileage Plus member). Frustrating, as it's been going on for hours now (was fine yesterday).
If you need urgent access, call them! +1 866 953 22 94 is the US helpline for the app and LH.com