We are aware of a bug that causes these two error codes when multiple login windows are open.
When you open a login form on Twitch, we give you a cookie with a unique value that helps us verify that you’re still you when you complete the login flow. If you open multiple login forms, the cookie’s value gets overwritten by each form after the first, causing the errors you’re seeing when submitting any but the most recent of the forms.
We are investigating clean solutions to this but do not have an ETA for now. In the meantime, hopefully that information can help you – ensure that you’re not opening multiple login forms at once.