The HUD is not refreshing. It shows people are on calls, when in actual fact the call is finished & they're not on a call any longer. The only resolution I can see is logging out of the app & then logging back
We had one known instance of this occurring in our office yesterday as well. The HUD showed a person was on the phone, but the person was not. The only way to update the HUD was to log out of the RC for Windows App and log back in.