You can add me to the list of users having problems with ATV 3 since IOS and Yosemite.
Random disconnects to the main menu when trying to watch movies via my iMac and home sharing. Weirdly, things such as Netflix continue to work fine, but it will fail to reconnect to my library and just sit on the spinning wheel.
Rebooting the ATV and iMac still won't make it reconnect to iTunes, but a reboot of my router does. I've tried fixed IP's, DNS changes, IP reservations and none have solved it 100% both wired and wireless. Sometimes I get dropped once other times five or six times during a movie.
Frustrating to say the least.
After a rocky beginning, I had managed to maintain a trouble free apple tv experience for a few years and then immediately after the Yosemite upgrade I started having home sharing problems all over again. I said screw this, life's too short for this crap. I ran a time machine restore back to Mavericks and I've been trouble free since. I run Yosemite on my laptop and it's fine but my iTunes server (mini) needs to be rock solid. I check in on the forums occasionally to see if things have been sorted out.