Steps to reproduce:

1. Open the attached CornellBox project
2. Begin baking with CPU Lightmapper
3. Immediately swing the camera left-right a couple of times
4. Switch to GPU Lightmapper -> CPU -> GPU
5. Turn off auto mode
6. Turn auto mode back on
7. Crash

^^ This reproduction procedure is not 100% reliable, but a permutation of these steps will always end up in a freeze and crash. For example, you may need to switch lightmappers an extra time.

OR
1. Bake lightmap on CPU in auto mode.
2. Switch to GPU
3. Uncheck auto (will trigger a call to cancel).

Reproduces in: 2020.2.0a19, 2020.2.0a18, 2020.2.0a12
Does not reproduce in: 2020.2.0a07, 2020.2.0a8, 2020.2.0a10, 2020.2.0a11