Summary: To detect this cause, in a CMD window: ipconfig /all. Look for Node Type: if it's "Unknown" then try this:
Change or create: dhcpnodetype, DWORD, 8;
and NodeType, DWORD, 8.
Bounce the LAN interface (in Network Connections, disable and re-enable.) ipconfig /all, Node Type should change to Hybrid.
If you're remote-controlling thru the same interface, you'll have to restart Windows instead, since you'll lose connection when you disable the interface.
Does anyone have a way to bounce and interface with a single command?