The light in the Blueprint Editor's Preview Scene does not respond to any lighting channel but 0.

In the Blueprint Editor, Primitive Components can be configured to respond to Lighting Channels 0, 1, and/or 2. However, if channel 0 is disabled (even with another one enabled), the Preview Actor's component in the Viewport Tab will be completely unlit, which harms the usefulness of the preview. This happens because the Directional Light inside the Preview Scene used by the viewport is configured by default to respond to Channel 0 only, and there does not seem to be any way to change that.

A quick-and-easy fix for this problem would be to configure the Preview Scene's Directional Light to respond to all lighting channels (Engine\Source\Runtime\Engine\Private\PreviewScene.cpp:76).

A better fix might be allowing the user to freely configure the Lighting Channels of the Preview Scene's Directional Light, similarly to how the Preview Scene can be configured to some extent in the Static Mesh Editor and the Material Editor, for example.

• Open any project
• Create an Actor Blueprint
• Edit the blueprint and open the Viewport tab
• Add a "Cube" Static Mesh Component
• Select the cube and change its "Lighting Channels" to only 1 or 2
• The cube in the viewport will be unlit with no way to change that