I tested this further and found that the same issues occurred with other UPnP Servers and clients on the same hardware, but that the problems didn't occur when using a different PC as a server. This would seem to imply that the issue is networking or firewall-related.

I'm not sure of what the problem is exactly, but this might be a good starting point:
https://techtourguide.wordpress.com/2015/01/15/optimizing-wireless-network-for-chromecast/

-Rusty

Thanks--I've replicated and re-opened the issue.

-Rusty

I'm having this exact problem since this morning, everything was fine up to yesterday: http://www.ventismedia.com/mantis/view.php?id=14032

Abettik