I have struggled with Synology media server myself and found a solution that I decided to share on a forum, as forums have been helpful to me. Note that I have a DS 8 series but the issues are the same as for the 2 series. 1) My (panasonic) TV always took around 5 minutes to find the media server , 2) sometimes just couldnt find it at all and I had to stop all users and/or take power of modem/router and 3) sometime my TV stopped seeing the media server after I used another device elsewhere in the house to approach my DS. Clearly a pain in the b*.
The same applied to my Yamaha Receiver, it often couldnt find the media server.
Additional strange problem, I had an apple TV box connected but my apple machines couldnt find that airplay anymore and when they would (after a full reset) , then I couldnt find the media server anymore on my TV. To pull your hair out. It did make me think that it was a problem with DHCP, the assigning of temporary local IP addresses to all these machines/users. But.....my Synology firewall was already off (you dont need it when you work through a router from a provider with its own firewall) and also I had already given my Synology DS a Fixed IP address (this btw is important).
Then a friend of mine (IBM guy) mentioned that the Router provided by my all-in internet-TV-telephone provider is of soso quality especially where it comes to finess in the protocol software. He told me to reinsert my very good Netgear Router (a somewhat higer end model, Euro 150) between my modem/router from the Provider and my (wired) users. Its a good idea to wire from your router to your TV anyway if you watch HD movies. And....VOILA !! It all worked on the spot !! Bonus, my airplay also works fine now. So it can indeed be the quality of your router and its software that deals with all these users that want to approach each other and communicate with each other including communication like DLNA, airplay etc.!
My solution was very simple actually. Network cable from one of the outlets of my provider's modem/router to my netgear router (one of the 4 LAN ports), Synology network cable to one of the 4 LAN ports and my living room network cable to one of these 4 ports. Powered up and it was done (the netgear had already a configuration from when I used it few months before). Note that the Netgear router took over the router function so the users had to switch to that router and that password. Hope this helps some of you.