I’m using lock v10.20.0 and whenever I set a prefill value for the email it is only filled out in the sign-up form. I also need it to be set at the sign-in form.
Using v11.1.2, we have been able to get this “prefill” option to work for our sign-in form using the embedded Lock. Our use case is to have the email prefilled for subsequent authentications once they have initially authenticated using it.
If this simple script does not show you the email prefilled in both the signin and signup fields, you can check your console log for any errors. Another option is to try it in other browsers to see if the behaviour remains.