Hyper-V Guest: Upgrade from 10.3-RELEASE to 11.0-RELEASE breaks networking

10.3 was perfectly happy, but after upgrading to 11.0-RELEASE (11.0-RELEASE-p1), neither the synthetic hn0 NIC nor the emulated de0 NIC are working.

I see from the release notes that some work was done on hn_netsvc, but I don't see anything that would cause it to stop working.

Host is Windows Server 2012 (not R2), and all the other VMs on the system are fine, including a guest still on 10.3-RELEASE.

It appears that the NICs are unable to send, but are able to receive. tcpdump shows the NIC receiving broadcast traffic, and IPv6 SLAAC works (the NIC picks up a v6 address and knows the address of the router), however, when trying to send traffic there are no ND or arp packets seen in tcpdump or on the wire. dhclient complains:

freedom dhclient[pid]: send_packet: no buffer space available

I can confirm that this problem also occurs with a fresh install of FreeBSD-11 from the ISO.
I have the same issue :(

I am try to install new virtual machine from FreeBSD 11 ISO image, but without success.

On Microsoft Hyper-V server 2012 R2 is working perfectly!