Airplay no longer working on iTunes 11.1.3 Windows 8.1

I have a PC connected by ethernet cable to a router, which is sending a wireless IPv4 signal to an airport express on my home network, which is in turn connected to some speakers. I also have an Apple TV connected to the same network. Airplay worked fine in the previous version of iTunes, but since 11.1.3 airplay no longer works properly.

On a fresh reboot of the PC & opening iTunes, the airplay icon appears, and airplay works as normal. However, after an arbitrary amount of time (usually between 3-10 minutes) the airplay feature becomes unresponsive, and the only way to remedy it is a fresh reboot of the PC.

However, I can play music from my iPhone through the Airport Express to the speakers, and I can mirror audio from my macbook through the AE to the speakers, but iTunes can't see anything with airplay (no speakers, no Apple TV) and the remote app on my iPhone iOS 7 can find the Apple TV, but can't find my shared library on the PC. So it's not a proble with the AE, or with the router.

Other PC users with a similar issue who are connecting to their router by WiFi have reported a that turning off IPv6 appears to be a usable workaround, but I can report that it does not work for me when connecting to the router by ethernet cable.

Also, the Airport utility can see the AE after a fresh reboot, but again after a few minutes it can no longer see the AE.