Bank of America

Ah ha! So it turns out my password was 24 characters long, and the way 1password auto-fills out the password overrides the client side javascript and enters in the 24 character long password, which passes 24 characters to the server-side password checker, which then fails, likely simply due to the password being too long. If I paste in the password, the client side javascript ignores the extra characters and so the server only sees the first 20 characters of my password.

After logging in, I went into my account and changed my password to something 20 characters long, logged out, and then used the autofill. Which works!

Thanks for helping, totally clued me into the problem!