Steps to repro:
1. Open the attached project and 'ProgressiveLightmappingExample' scene on OSX;
2. In the Lighting window press the dropdown near the "Generate Lighting" button and select "Clear baked data";
3. In the Lighting window press "Generate Lighting" button;
4. When the GI baking is finished, change some lighting-related settings (e.g. type '1' into "Direct Samples" field);
5. In the Lighting window press "Generate Lighting" button.

Expected result:
GI baking finishes without errors.

Actual result:
Editor crashes instantly. The stacktrace is meaningless. See attached video.
Regression introduced in Versions 2020.1.3f1 and 2020.2.0a21.

Notes:
- Reproducible in Version 2020.2.0a21, 2020.1.3f1;
- Not reproducible in 2020.2.0a20, 2020.1.2f1, 2019.4.9f1;
- Reproducible only on OSX, not reproducible on Windows;
- Reproducible only when clearing baked GI after initial bake;
- Reproducible only in the attached project; not reproducible in the URP sample scene and in the CornellBox project;
- Reproducible only when baking with PLM; not reproducible when baking with Enlighten;
- Could not test on GPU PLM because the GI bake cannot be completed (known issue);
- Sometimes when the crash happens (1 of 5 times approximately), the Editor freezes, and the only way to close it is to restart the machine (killing the process from the macOS Activity Monitor has no effect). However, the frozen Editor doesn't freeze the whole OS.