How to reproduce:
1. Open attached project "2018_2_Test"
2. Open SampleScene and in Lighting settings window turn on Baked Global Illumination in Mixed Lighting tab
3. Generate Lighting
4. Observe the cubes emitted light onto static surfaces
5. Look at Light Explorer window Static Emissives tab

Expected result: Both cubes emit light onto static surfaces when Generating lighting. Both emissive materials are visible in the Light Explorer window's Static Emissives tab
Actual result: Cube with ShaderGraph's PBR shader does not emit light onto static surfaces and is not visible in the Light Explorer window's Static Emissives tab

Reproducible with: 2018.1.9f1, 2018.2.1f1, 2018.3.0a3

Note: LWRP and ShaderGraph was introduced in 2018.1 also could not reproduce with 2018.3.0a5 due to another bug (case:1061360)