I think I MIGHT know what it is. This same problem is still happening to me. I think it might be because I am game sharing with a friend on ps4. Which you probably know, means that my friend's account is chosen as "primary" account on my ps4 and my friend is the one who did the actual purchase of beyond light. My friend does not have any friend roster issues but I do. Interesting thing is my friend's username starts with the letter D and my friend roster only displays players with the usernames that begin with the letter A through C. Any username that starts with D to Z are not listed. It will show that I have 20-30 friends online but only A through C are inspect-able and/or joinable which is like approximately 5 of those players. Another thing is that I have a 2nd account and my 2nd account does not appear to have any friend roster issues. So I don't know, maybe this is some food for thought.