In the alumni profile, if the lifetime email address (@alumni.duke.edu) is marked as 'preferred' there will be no email address displayed in the 'Contact area of the About tab of the profile. Users can see emails in their own profile, but other users will not see an email when looking at another user's profile. This is not a bug related to privacy setting, as other addresses (Home or Work) marked preferred will display in the Contact block.
The team is working on resolving, but no ETA is set for it being fixed.
We are pushing a fix to production on 4/8, and will begin running the processes to add back in the 'contact' button on affected profiles once the code fix is in place.