I have seen that mdns is not working reliable when a connection is established over wifi. In my special case I am using the Chrome Browser and Chromecast to mirror my PC. But often the Chromecast receiver is not visible with in the browser.
With wireshark I can see the MDNS queries sent from the windows device but I don't see the mdns broadcast on the other devices. So the upper layers in windows are sending the query but it never leaves the wifi interface.
But when I change some properties in the windows system-settings for the wifi card suddenly I can see the queries also on other devices but only for a short time.
In my setup I'm blocking SSDP (Port 1900) to be sure that only mdns is used for device discovery