Thank you for the post. Searching on our downloadcenter site there is no Windows* 10 driver for I219-V network. Onboard NIC are to be supported by the board vendor as they are the one to customized the drivers to adapt to the system. You may further check with Asus* support regarding this issue.
Have reported this to Asus & I'm waiting for some feedback from them.
I've got the exact same issue on my newly built Gigabyte GA-Z170-UD3 + i7 6700k system. Slow performance, random disconnects, especially on the steam. Very curious.
No answer? I also have an open ticket.