Hello,
I am seeing this exact same issue. I have enabled uPnP on my pfSense router. I have installed the uPnP integration in Home Assistant as well (although, not sure if that is supposed to make a difference).
But whatever I try, the Echo devices just do not discover a new device I have added to emulated_hue. (Previously discovered devices work fine, though)
http://<HA IP Address>:80/api/pi/lights shows the new device.
Any ideas?