I'm not sure if y'all have had any luck as this is an older thread, but this happened to me yesterday and I was able to determine why. When I was moving server files from one machine to another, I initially forgot to retain the original basic.cfg and config.cfg files. While the new machine was trying to use the basic.cfg from the old one, I would be instantly kicked with this type of message in the log:
6:17:25 NetServer: cannot find channel #578289351, users.card=0
6:17:25 Message not sent - error 0, message ID = ffffffff, to 578289351 (Colonel Angus)
Once I restored the new machine's basic.cfg and config.cfg from when I used to run a successful Arma 3 server there, I was able to log in and play without issues.