Reproduction steps:
1. Open the user's attached "OpenXROculus.zip" project (can be found in case 1326119)
2. Load SampleScene
3. Make sure OpenXR is set to "SteamVR runtime" and Graphics API to Vulkan
4. Enter Play mode

Expected result: only one cube is rendered for each eye
Actual result: two cubes are rendered for each eye

Reproducible with: 2020.3.3f1, 2021.1.2f1, 2021.2.0a12

Notes:
- not reproducible with DirectX 11
- not reproducible when using Multi-Pass rendering mode
- could not test if the same issue occurs with Oculus Runtime due to crash in case 1324478
- could no test with Oculus XR plugin because it supports only DirectX 11 graphics API

Tested with Oculus Rift and SteamVR 1.17.4