Operating system: Windows-10-10.0.16299 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 419.67
Broken: version: 2.81 (sub 4), branch: master, commit date: 2019-08-28 20:33, hash: rBa7ac8a22f8eb
Short description of error
When "Transparent" is enabled in "Film" tab, denoising (old blender denoiser) is producing dark pixels. It seems to happen only with an environment map. When "World" is set to flat color, problem disappears. Here's an example (zoomed in):
There seem to be holes in "Denoising Depth" pass which seem to coincide with the bad pixels.
When you turn transparency off, those artefacts disappear:
Denoising Depth also looks a lot cleaner, although there are still couple of bad pixels:
Here's a file with the example above. It has env map packed in.