System Information
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 1070/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 451.67

Blender Version
Broken: version: 2.90.0 Beta, branch: master, commit date: 2020-08-25 16:00, hash: rB21cb6f09ffa8
Worked: (newest version of Blender that worked as expected)

Short description of error
Flat planes that contain alpha transparency will create black artifacts when they overlap within cycles.

Exact steps for others to reproduce the error
When using a typical workflow for creating things like low poly grass, whereby multiple planes containing alpha transparency are duplicated and close together, there's some pure black artifects that appear in the overlap, but not just within the overlapping planes - It also appears when looking at one 'collection' through the alpha'd areas of another. As though the alpha part of the plane is not entirely devoid of visual information. Sorry I tried really hard to describe that but it's instantly noticable visually.

Effect is entirely absent in Eevee and only shows up in cycles. Using the attached file and with cycles activated, pan around the grasses and you'll see. Try looking at the white grass while looking through the alpha areas of the other white grass. And in general, just pan around the grasses.

Blend modes/shadow modes are, to my knowledge, correctly configured.