A few things:
1. Log into the NAS and ensure under application management, UPNP is enabled
2. Ensure a proper folder is selected and refreshed
3. DLNA implementations are finicky as best so once it's refreshed, restart your TV and search for media servers, select dlink-xxxx and try again
4. If you see no content and you've shared a lot, try narrowing the folder down to a sub folder. Sometimes doing a drive with 1000 movies and 100000 songs may give issues
5. DLNA implementations from Samsung, Sony etc isn't always that great. The software they provide usually is the only one that works well and probably the only one they will support. Defeats the purpose of DLNA.
In my experience it seems TV/Bluray vendors put DLNA support as the lowest priority and it seems to be getting worse. The priority is app quality and quantity + on demand paid movie ecosystems. Online paid content = revenue.
You could also try using their software and pointing the share folder to your NAS. It's not ideal but it's a stop gap.