If you use an InstancedStaticMeshComponent and enable
bUseGpuLodSelection=true
r.InstanceCulling.OcclusionCull 1
and you have instanced stereo enabled, then all the culling of instances happens based on the left eye only, and any instances that would only be visible in the right eye are missing in the right eye. Disabling instanced stereo fixes it.
Would be nice to get this fixed, since the ISMC GPU LOD+Culling is actually a very nice feature.