Artifacts after baking GI with certain lighting settings and denoising enabled

Steps to repro:
1. Download the ArchViz Pro vol.6 project (link attached in the comments) and sync to revision `8546d9d7f07d` of the 'DenoisingBug' branch;
2. Open 'AVP6_Desktop' scene;
3. In the Preferences window (Edit>Preferences>GICache tab) click "Clean Cache" button;
4. In the Lighting window (Window>Rendering>Lighting) press the arrow button near the Generate Lighting button and select "Clear Baked Data";
5. In the Lighting window press Generate Lighting button;
6. Observe the Game View window after the baking is completed.

Expected result:
The scene with baked lighting is rendered smoothly without artifacts.

Actual result:
There are artifacts on the baked geometry's surface. See attached .gif video.
Regression introduced in Version 2020.1.

Notes:

• Reproducible in Version 2021.2.0a17, 2021.1.8f1, 2020.3.9f1, 2020.2.7f1-dots, 2020.1.9f1;
• Reproduces unstably (sometimes) in Version 2020.1.8f1;
• Not reproducible in 2020.1.7f1, 2019.4.27f1;
• Reproducible on Windows (NVIDIA GeForce RTX 2080Ti GPU);
• Reproducible only when baking with GPU Lightmapper; not reproducible when baking with CPU Lightmapper;
• Reproducible when baking GI with Optix or OpenImage denoiser enabled; not reproducible when baking GI with RadeonPro denoiser enabled;
• Not reproducible when denoising is disabled;
• Increasing direct samples to 512 and rebaking GI fixes the issue;
• Artifacts are visible in both Shaded and Baked Lightmap debug Editor visualization modes.