my friend has two PS4's, one is the one he plays on and on other one he hosts a custom in which he joins with the 1st PS4. But after 10 - 15 minutes, one of his PS4's disconnects (error-code: bat).
We followed the guide from Bungie to have two consoles in the same network [so we disabled port forwarding and enabled upnp]. On the main router (the one that dials into the internet) Netduma R1 is setup as an exposed host.
TL;DR: Disconnects appear 10 - 15 minutes into a custom game on one of the consoles.