Steps to repro:

1. Create a new project;
2. Add a cube gameobject;
3. Mark the cube as static in the Inspector;
4. In the Lighting Window untoggle Baked Global Illumination checkbox while baking lighting.

Actual result:
Assertion:
'Assertion failed on expression: '(int)indices[kStaticLightmap] + staticOffset >= 0 && indices[kStaticLightmap] + staticOffset < kLightmapIndexInfluenceOnly'

is shown in the Console. Regression introduced in 2019.3.0a1.

Expected result:
No assertions are thrown when switching lightmap backend.

Notes:
- Reproducible in 2019.3.0a12, 2019.3.0a1;
- Not reproducible in 2019.2.2f1, 2019.1.14f1, 2018.4.6f1;
- Reproducible only on Windows, not reproducible on OSX;
- Not reproducible when switching from Enlighten to PLM.