To reproduce:
1. Open attached project;
2. Open "DemoSceneBlank" scene;
3. Go to Player settings (Edit > Project Settings > Player) and make sure VR is enabled, Stereo Rendering Method is set to Single Pass Instanced;
4. Enter Play mode;
5. In the Panel on left, you'll see a drop-down which says "No Clouds", set it to any other value (f.e. Heavy (Dark)).

Expected result: Command buffers renders clouds in both eyes with Single Pass Stereo Instanced method.
Actual result: Clouds are rendered only in the left eye.

Note: tested and reproduced on Oculus, OpenVR, Mock HMD - Vive.

Reproduced on: 2017.3.0b1, 2017.3.0p2, 2018.1.0b2.
Not reproduced on: 2017.2.1p1, 2017.3.0a7.