The only thing that changed as part of 1.4 was the active user limit for watched content. This is not related to conversations.
If conversation emails aren't going out and you're sure they should be (based on config), that would imply that all mail is broken. If nothing changed, you may want to contact your host about it (or your SMTP provider, if you're using an external SMTP server). Alternatively, you could try changing mail to be sent via SMTP (though this isn't preferred).