The email attribute cannot be retrieved from the Group members API

Dear Sir

I noticed that when I used this Group Members API I was not getting just the email attribute.

I checked the reference and it said that the email attribute was restricted to be retrieved and that it could be retrieved by setting the user’s email status to public.
[ Limitations
The email attribute is only visible for users with public emails.]

However, I set the email status to public in the user’s settings screen, yet I could not retrieve the email attribute.

Is there any possible cause for this?
See similar to the following question.

Kind regards