Edit: This issue was introduced with this commit https://developer.blender.org/rBa7cd05d15028dc71d341bf21ca6b49dcf3b9e784
I found a bug.
The reflection of emmissive trianges in rough glossy surfaces isn’t working properly when Many Lights Sampling is On. It easiest to see at low roughnesses.
Here is a .blend file I used for testing:
Renders
This is a simple scene. I have a ground plane, fully metalic and a little bit rough. And an emissive plane. As you can see when Many Lights Sampling is On, the reflection of the plane renders incorrectly. Increasing the roughness hides the issue, and decreasing the roughness to 0 resolves the issue.
Many Lights Sampling Off:
Many Lights Sampling On:
