We have not altered the permissions for the administrator group that I am in. The last time I logged in it was working just fine but now for some reason I am unable to see this tab.
If your site has multiple centers this could be the issue. Often this will occur when an admin is in a group where Contact Management permissions are tied to a specific center. If you are seeing this issue while in all centers mode, try switching to the center that Contact Management is associated with to see if this resolves the issue.