I'm encountering a number of issues with the friends list management.
Firstly, it would appear that accounts are being added to each other's friend list automatically. I've noticed this with accounts that are friends on Steam. I'm not against this per se but is this expected behaviour? I haven't sent any AddFriend requests as of yet.
Regardless, when trying to remove this entry either via the client API or the dashboard, it fails (AccountNotFound on client (sent the PlayFabId) and a blank error on the dashboard). So, if it has been added automatically, it presumably hasn't been added completely - enough to appear in the GetFriendsList request but not enough for RemoveFriend.
I'm noticing this on my dev title (429FA) with accounts 588BAED7A29F0CA2 and 98664FFE05647526.