If you turn on Stereo Instancing in 4.11, and you turn Anti Aliasing OFF or set it to FXAA, all your transparent objects that are instanced by default (Instanced static mesh actors or Hierarchical Instance Static Mesh Actors) are rendered wrong in your left eye.
For example transparent foliage will look wrong.
The translation of the instanced objects seems to be off for your left eye.
Here is a repro case:
Start a new Default scene (Not an empty one)
Enable Stereo Instanced rendering in the project settings.
Add a piece of terrain.
Add a piece of foliage that includes transparency.
Add a post process volume
Set the volume to unbound
Disable or set the AA Setting to FXAA (Under Misc)
Preview the map in VR
Now you can observe that the left eye doesn’t render the foliage as it should.