some kind of region issue perhaps?
Just a guess, but you might adding players via the website that are not Stadia players, and Destiny does not currently offer cross-play. Stadia only, for now.
I wasn't seeing members of the clan I'm in until I was also Stadia friends with them.
@TheRealAnorak I hope you can get a workaround on these forums however I am pretty sure this is a Bungie issue.
You know what I even remenber having a simmilar bug when they launched it on PC a few years back.
Good luck.
Good point there, Ant. Check your privacy settings for friends, AND, make sure you enable Publisher access.