Skype contacts shown as Unknow users

Hi, 

I'm using teams, and everything working fine. In our company we have some kind of integration of Skype with teams, forcing us to talk though teams even if some contacts in other organisations r using Skype. Last couple of weeks there are some contacts that r shown as Unknown Users, they can speak to me but i can't reply them i just can see their status.

Strange thing i have this issue but other guy in my organisation, can talk without problem with the same contact.

If i have them in my contact list i can see status and name, but if i try to start a conversation Unknown Users show up and the messages can reach them.

I cant't connect this behaviour to another threads even with the same issue (Unkown User)