Reproducible on 5.2, 5.3, 5.4.

In Build Settings enabling "Unity C# Projects" option, SyncVar is not updated on UWP platform client or server side.

Repro steps:
1. Open project "Multiplayer.zip". (in edit there's a smaller repro attached)
2. Build to UWP platform.
3. Launch project in the editor. Create local LAN host or enable match making and create internet match.
4. Build and run UWP project. Launch "Lan Client" or in "Match Making" find created internet match.
5. Press arrow keys in the editor to move the cube. Now press arrows in UWP project. Observe that "opponent" cube doesn't get synchronized. Launching the same scene on windows standalone, opponent's cube is synchronized as expected.