I think it is a good alternative to get around this situation so there is no need to put a wait time for mIRC to enter the channels if we have an option that we can activate or deactivate in the favorite mIRC dialog for example:

(check) Only after identification

and with this active option, mIRC only entered the channels if it returned from the identifier $usermodes the mode +r that corresponds to the identification of the nickname.

irc.PTirc.org (IRCop)