Shelter - Guardian Heal skill
I believe they’ve actually commented on this one and that it’s intended. Might have been during the livestream where they showed off specializations for the first time. I’m not sure.
It is not part of any group since all the other groups have cooldown/effectiveness improvement traits. If the skill was put into a group, the base ability would have to be made worse to compensate for the extra power from traits. Instead of making it worse and requiring a trait to make it better, they just left it alone.