When mIRC requests several IRCv3 settings, it won't send CAP END until it gets an ACK response for all of them. I'm guessing that ZNC intercepted either mIRC's request or the server's response. So either the server never saw 1 of mIRC's requested items, or ZNC stripped one of the 'words' from the server's ACK response.
So you might need to stop ZNC from interfering, or make mIRC stop waiting by doing something like:
on *:LOGON:*:{ .timer 1 2 raw CAP END }
... with optionally using $network or $server or $servertarget to limit when this activates.
Last edited by Khaled; 24/03/23 09:52 PM.