Can you please explain the solution? im having similar problem
Basically, Server Armour doesn't utilise the bans.cfg file for its ban/unban. Rather it caches every player locally in the oxide/data/ServerArmour directory. So if you want to use SA on your server, you should do all the ban management through SA and not via RCON (it will cause problems), so avoid that.
You can only ban/unban players who have been "seen" by SA, i.e. those who have connected to the server and been cached.
If you ban on one of your servers, it is stored remotely on the SA website database where all your servers are grouped under you're SteamID login, so acts to ban globally over all your servers if you have more than one
I believe.
If you go to the #bugs channel on ServerArmour Discord you will see the message history with useful info between me and a helper in the channel.