Hi,
Bungie is aware and are investigating the issue. I've underlined the temporary work-around for you.
[url]https://www.bungie.net/en/Help/Article/44670[/url]
[quote]Bungie is investigating an issue where the in-game Friends list on the Roster page may intermittently not populate for some players. [u]If this occurs, please join your desired Fireteam through the Friends list on your console user interface. The leader of your desired Fireteam may need to set their Fireteam Privacy Setting to Public until you have joined.[/u][/quote]