Well, funny this.
I've been having a disconnection issue when I use P2P software. I've been dealing with it for about a month now.
Finally Googled about it and sure enough the second result was this thread... which was made 2 years ago.
I haven't had this problem before and I've been using the Intel NIC for many months now. I used to use a Killer 2100, but it's had a problem where it breaks P2P connectivity for some unknown reason (I and Bigfoot have never been able to discover the issue; nothing but a full Windows OS reinstall fixes it) so I stopped using it last year.
Why it's suddenly disconnecting when it hasn't before, I don't know, but the fact that issues with this NIC has existed for a while is incredibly disheartening. Hopefully ASUS (and other board partners) use better quality NICs on future boards. Shame I'm limited to PCI due to needing to use a legacy card, else I'd grab one with an integrated Killer (though that may backfire if the eNIC still has the P2P issue the dNIC does)