I can’t seem to find a proper way to report this so here it is.
I was trying to login to eu dot battle dot net. When prompted for email and password, I used the saved values in my Firefox browser so it was prefilled. Password was incorrect, however.
When I entered the correct password, I was redirected to the authenticator screen, but it would take me back to the login screen again, I literally had no time to authenticate myself through the phone.
After refreshing the login screen page and entering the password correctly on my first attempt, authenticator screen was working properly.