Yeah It happens to me too sometimes, when i Reconnect I have Strict NAT again, then I have to tear open my modem all over again and open all the ports.
I have an Open NAT it makes no difference, the host migration affects everyone in that game and is not down t anyone else other than the Host. I get Host Migrations ALL THE TIME, I'm frankly p***ed off with it.
been happening to me since last Wednesday....bascially make it through the whole match then boom...."disconnected from LIVE"...only happens when I am made host