Steps to reproduce:
1. Open the attached project
2. Open the Main.unity scene
3. Go to Build Settings -> Player Settings -> XR Settings and select Single Pass Instanced (Preview)
4. Play the scene
5. You will see the capsule on the scene which drops the shadow
6. Point the gazer pointer right in the middle of the shadow and compare a view from left and right
7. Observe the offset of the shadow between eyes (You can compare with Multi Pass, it works correctly with Multi Pass)

Actual results: Shadows for any object (not just the controllers) render at different locations for the left eye than the right eye only when Single Pass Instanced (Preview) is enabled
Expected results: Shadows for any object (not just the controllers) should be rendered at same location

Note:
Reproduces with some GPU only. I was able to reproduce with NVidia GeForce GTX 1050 TI

Reproduced with: 2017.2.1p2, 2017.3.0p3, 2018.1.0b3, 2018.2.0a1