According to Reddit user eternal70200 once you launch two The Division 2 copies and try to join a group on the same network, or same external IP adress, the enemies in the host's world completely freeze and cannot be interacted with.
UPDATE: Ubisoft officially confirmed that the issue has been resolved.
Original Story: Ubisoft's looter shooter The Division 2 has finally launched today - 12 March 2019 for Gold and Ultimate Edition owners, and while many players are enjoying the post-apocalyptic streets of Washington DC, some have encountered game breaking issues that are preventing them from playing the game in co-op.
Reddit user eternal70200 reported an issue that occurs once two The Division 2 copies are launched at the same time on the same network or same external IP.
According to Redditor's post, he attempted to join a group for some co-op play but once he succeeded, the enemies in the group host's world stopped moving, making it impossible to shoot or hit them. However, the host was still able to search for loot and see the objective updates.
"Basically whoever joins the other player's instance takes over their instance and the host becomes a ghost with no interaction on their side." eternal70200 wrote in his post.
He also said that he didn't encounter the problem during the beta which suggests that one of the patches that Ubisoft released between the beta and full release probably bugged the netcode.
Luckily, the workaround for the issue has been found and if you're encountering the same problem, try to exit the game using Alt plus F4 keys and then launch the game again. You should still be in a group and for some reason, two instances should sync properly.
Of course, this is just a temporary solution until Ubisoft addresses the issue. The good news is that the problem has already been reported on Ubisoft's forum, and the developers are working on a solution.
The problem could be connected to UPNP setting in router configuration, as some players report the same issue in other games like Apex Legends and Rainbow Six Siege.
According to Redditor edgardcastro, disabling the UPNP setting should solve the problem, but you should probably wait for the official patch before you start messing around with your router's settings.