The only reason I thought that was because I know the regular IRC servers behave different if you connect to a channel your account is already in. It won’t send the channel users through a 353 response, it will eventually send them all as individual JOINs.
I’ll let you know if the delay doesn’t work, but it doesn’t look like this is a common issue, so it must be something I’m doing, although the same connection to irc.twitch.tv has never gave me any trouble.