Routing will break it unless you really dig in and figure out how to get multicast routing to work properly (I've never taken the time to figure that out completely myself). The default gateway isn't really important when it comes to UPnP/DLNA, since it basically only works on the local subnet. I would make the right choice some times, the wrong choice at other times - but be confusing for the user at all times. When it comes to using the routing table to select network interface, I don't think it's worth the effort. If they are supposed to be hidden, they aren't very well hidden as UMS enumerates them. From their names, there were one or two that looked to be physical adapters to me, but with no assigned IP address. What confuse me a bit is when I read the log, there are more than 20 network adapters (mostly virtual obviously). I doubt that is the issue here though, as I think that's the kind of issues that give unstability, not a complete failure to connect. I think it was something with buffering or queuing that isn't properly implemented creating problems. I know there have been some problems related to using virtual adapters, but I don't remember the details, which virtual adapters etc. Not that it's relevant here, I'm just saying that the fact that it's "the Microsoft way to do it" doesn't mean it's fully compliant. Microsoft has always had trouble following standards properly, I as far as I know there's some quite basic TCP/IP implementation details that's actually not to standard in Windows. Most of my VMs are non-Windows anyway, so it wasn't very tempting to use anything from MS as a basis - considering their track record for how things mysteriously stops working without explanation when it suits them. I haven't tested Hyper-V, but I'm quite used to virtualization, primarily via ESXi. How does UMS pick the interface to bind to? Is there a way to override it? The 192.168.56.1 is actually the VirtualBox virtual NIC. It has the 0.0.0.0 network destination paired with 0.0.0.0 network mask, has a gateway (important for routing) and has the lowest metric (if anything else equal, the lowest metric is used).
Is UMS running on a VM, or on the host itself? How is the virtual adapter connected to the rest of the network? It could be that there's a firewall running on the virtualization host even if the WIndows firewall is off, blocking incoming traffic but allowing SSDP (multicast discovery).
Since your TV can see UMS but can't list any content, it doesn't seem like the problem is with multicast though, since multicast is used for discovery while unicast is used for "everything else". Or, more correctly, if there is the router must be properly configured to also route multicase traffic. It might not be the case here though, but it is important that there's no router - virtual or not - between UMS and the renderer. That might be ok, but I know there's been issues earlier with virtual adapters not fully implementing multicast or having other "non-standard" behaviour. There is no valid address for any physical NIC, which means UMS ends up binding to a virtual adapter. I can't see anything obvious in your log except that I'm confused by your network configuration.