Packet loss when playing from one IP address

Has this issue not been fixed since the very beginning?

When I play with my son, using the exact same public IP address, either he or I experience packet loss. We have PCs with identical specifications and a 1 Gbps fibre-optic internet connection, yet sometimes one of us experiences around 36% packet loss.

It seems somewhat random. We don't both experience packet loss at the same time - It affects either him or me

btw. My ping to Frankfurt is 23-24ms consistent