GOOD NEWS! I figured it out. Posting the solution here as I’d be shocked if this didn’t come up again multiple times in the future with new ROCK builders using Windows 10:
In the Fall Creators Update for Windows 10, Microsoft disabled SMBv1 by default as they consider it insecure. This is how the ROCK exposes itself on the network, so SMBv1 is needed.
It’s very simple to enable again. Scroll down to the third post here (second reply): https://social.technet.microsoft.com/Forums/en-US/9fd07a6b-62dc-40b0-995c-5a3a5d533150/how-to-enabledisable-smbv1-in-windows-10?forum=win10itpronetworking