Mine did the same the last time I played, I tried everything rebooting the router, opening and closing the ports, switching off the console and running the Internet test numerous times.
I then plugged in my old router and it went back to open so I left it with the old router still connected.
I had upgraded my router a few weeks ago so it's strange how mid match it just dropped, tbh the new hub I got was actually giving me slower connection speeds and higher ping so it's now confined to the junk cupboard.
It wouldn't be so bad but it was the first time I'd played Ghosts since Xmas, hope you get it sorted.