We cannot say for sure how you triggered such a situation, @ktaylor. But there are a few settings related with Password and Account policies that handles the lockout time, session timeout, and password expiration.
I recently logged out by accident, and tried to log back in, and keep getting the invalid captcha, also. Doh! n/m, I think it was defaulting to EU instead of US.
@miker1000
There were similar reports before of the same ‘invalid captcha’ when a user tries to log in to the portal. Clearing the browser cache helped with the situation.