Unable to blacklist bug

I've decided to post this on the forum because a GM ingame told me so, anyway the problem is I've encountered blacklisting bug which includes:

1. Only seems to affect 2 very offensive harassing players which i wanted to blacklist (blacklisting everyone else besides these two "anomalies" always work normally)

2. Every single time i tried to blacklist > add name, i always got "cannot find a character with that name" error despite :
a. They're online
b. They're not in my friendlist ofc
c. I don't have any pending friend request from them which i would gladly reject anytime
d. I won't write these 2 anomaly player's name because public shaming is not allowed here.
e. And no, they're not a RMT spammer characters, just a well known notorious, very bad reputation players in our server.