First, please attempt a to power cycle your modem/router. To do this please follow the steps below.
1 .Switch off and unplug the power from your modem/router.
2. Leave both unplugged for 30 seconds.
3. Plug the power back into the modem/router and verify that you are again connected to the Internet.
4.Once you have internet go ahead and boot the game and verify if this has fixed the issue.
If this does not fix the issue we have a work around that should fix this lobby issue.
1. Disconnect for your online partner and go into single player mode.
2. Make a bit of progress on a character that you have not gone through story mode with.
3. After a couple of levels save the game and attempt to connect online with your online partner.
If you are still unable to clear up this issue please submit a ticket and we will troubleshoot the issue with you.