I have similar issue and already opened another thread for it...no reply so far. So I'll give it a try in here.
I'm using a Mac Mini (Mid 2010) with 4GB RAM, Yosemite 10.10.2.
The Mac is connected by cable to a Gbit Ethernet network switch.
I hope the following drawing helps to understand the network environment:
Mac <--> Switch_1 <--> Switch_2 <--> Fire TV
Switch_1 <--> WLAN Router AVM Fritz!Box 7270 <--> 30MBit Internet connection
The Mac and the Fire TV (running AirPlay server App) are both connected by Ethernet cable, but to different switches.
No WLAN enabled on Fire TV.
The WLAN router is the DHCP server.
For sure the remote App is running on an iPad (2) which is using WLAN.
All network addresses are in same network and were provided by same DHCP server (running on WLAN router).
All my music and internet radio is coming from the Mac.
I use remote app (latest version from Appstore) on the iPad to connect to iTunes 12.0.1.26 running on my Mac.
In iTunes I selected the Fire TV as AirPlay receiver.
Fire TV is playing all music through my AV receiver.
This is working perfectly fine except one issue which exists since update to Yosemite 10.10.0.
It remained same with Yosemite 10.10.1 and 10.10.2.
My problem is that I need to enable WLAN (wireless) on my Mac since update to Yosemite.
When I disable WLAN remote app does not find my media library anymore and iTunes is unable to connect to the Fire TV.
When I re-enable WLAN, everything is working fine again.
Remember, all devices except the iPad are on a cabled 1Gbit Ethernet.
Before updating to Yosemite I did not need WLAN.
Any idea what's causing this? IP traffic routing issue?
Usually, when I disable WLAN on the Mac, it continues to run for 1 or 2 days where the iPad has no problem to find and connect to the media library.
After a while. running with WLAN disabled, my iPad is not able to "see" the iTunes media library asking me to enable home sharing.
When I check on my Mac, home sharing is enabled.
I then disable and re-enabled home sharing in iTunes and after doing so my iPads is able to "see" the iTunes media library but it cannot connect to it.
I checked routing and arp tables on the Mac but everything looked fine, routing through the Ethernet interface.
I used "fing" on the iPad to see which devices are online and "fing" on my iPad was only aware of the Mac Ethernet interface. No entry for the disabled Mac WLAN interface.
I checked on the WLAN router and ensured that both Mac interfaces have unique host names (aliases) on the router.
To be sure everything is refreshed I rebooted the router.
No change, my iPad was able to find the iTunes media library through home sharing but was unable to connect to that media library.
So I enabled WLAN on the Mac and immediately my iPad could connect to the iTunes media library.
Weird...
Only mitigation I found so far is to re-enable the WLAN on the Mac.
So I assume something is broken in Yosemite / iTunes 12 home sharing.