To reproduce:

1. Download attached project "FinalRWWin.zip" and open in Unity
2. Open "sample" Scene
3. Enter to Play mode

Expected Result: The cube is rendered to the RWTexture (the RWTexture is shown in the top left corner) when playing in the editor and when playing in the player
Actual Result: The cube is not rendered to the RWTexture in the editor or the player.

Note: Setting 'Shadows' to 'Hard and Soft Shadows' in 'Project Settings -> Quality' fixes the issue in the player, but not in the editor. Also setting 'Shadow Type' to 'Hard' or 'Soft' Shadows on the camera fixes the problem in the editor as well. Enabling 'Allow HDR' or 'Force Into RT' on the camera also seems to fix the issue for some reason.
Note: It should be backported to earlier version of Unity (5.6)

Reproduced on Unity 5.5.4p2 and 5.6.2p3
Not reproduced on Unity 2017.1.0f3 and 2017.2.0b3