Reproduction steps:
1. Open the user's attached "XR Plugin Postprocessing Bug.zip" project
2. Load the SampleScene
3. Enter Play mode

Expected result: Ambient Occlusion is properly applied (see "AO_expected.png")
Actual result: Ambient Occlusion is broken (see "AO_actual.png")

Reproducible with: 2019.4.24f1, 2020.3.4f1, 2021.1.2f1, 2021.2.0a9
Not reproducible with: 2021.2.0a10, 2021.2.0a12
Could not test with: 2018.4.31f1 (XR SDK not available)

Notes:
- reproducible both with Single Pass Instanced and Multi-Pass Rendering mode
- the issue does not occur when "Initialize XR on Startup" in Project Settings is disabled

Tested with:
- Oculus Rift
- MockHMD