Playing videos would result in "Device disconnected" 20-30 minutes into the file being played.
After this error occurs - Serviio was no longer visible from my TV (LG LM9600).
Only way to bring it back was to restart the tv, at which point I will get another 30min of play before I had to do it all again.
Another TV set (also LG) somewhere else in the house was working just fine.
All TVs are connected via hard-wired ethernet - no WIFI.
Trying various server side solutions (ie. modifying settings in Serviio, downgrading serviio, using other DLNA servers, etc.) did not solve the issue. Increasing the Serviio timeout value on SSDP simply deferred the problem but did not solve it. In other words, setting the timeout to 2 hours, meant that you could now watch a movie for about 2 hours before it fails, but it would still fail.
I decided to look at the network hardware. The only difference between the network setup of the two TVs was that the one that had problems was going through a D-Link router/switch, while the other one that worked flawlessly was on LinkSys. After doing extensive searching on the internet I found the hint to the solution on a Philips TV support site.
The issue turned up to be IP Multi-Cast protocol support by the router, which is needed by most DLNA/UPNP servers in order to effectivel;y advertise their presence. To make a long story short, some routers do not have multi-cast support turned on by default, or have an inconsistent implementation of this support. This results in exactly the kind of behavior I was experiencing (disappearing Serviio).
For me it was to turn on UPNP and IPv4 Multicast support on my D-Link router (off by default) - this in the Advanced>Advanced Networking tab. If still having issues - turn off IPv6 multicast support - and leave only IPv4 multicast turned on. This setting seemed to cause some issues for some folks.
The LG TV now works perfectly with Serviio.
If you see this issue on other routers, especially if you using DD-WRT or other custom firmware - I would recommend digging through the settings to find both UPNP and Multicast and make sure these are turned on.