Everywhere I look, nobody else seems to have this issue.

A friend and I aren't able to hear each other in party chat when we're alone. However, when someone else joins the party, we're able to hear each other just fine. We both have an open NAT type, and never had this problem as of a couple months ago. We've enabled port forwarding and DMZ, yet the issues persist. It doesn't end there though. We are able to play certain games where we CAN hear each other in the in-game group chat, such as Overwatch. Yet when we play another game, such as For Honor, we can't even join each other... BUT we can when there is another friend present. I'm positive there are other people that have the same issue. Is there any way we can fix this?