Where is the Sign up to our newsletter coming from? That's definitely not a part of JFBConnect. If you're using JomSocial (or Community Builder), you can show additional fields during the registration process, but that's not something we do without integration into another profile component.
Hope that helps, but if you can narrow down where that field is coming from on the other sites, that should help you to do it on the sites that don't have it.
JFBCLogin "Sign up to our newsletter" configuration
