Steps to repro:

1. Open SponzaLWRP: https://ono.unity3d.com/test-data/gi-tests/SponzaLWRP
2. Change to 4K lightmap size
3. Change to the lightmap resolution to 100
4. Set filtering to none (optix bug)
5. Settings: https://imgur.com/AV7qxEY.jpg
6. Clear Baked Data
7. Clear GI Cache (and make sure you have plenty of cache space available)
8. Bake
9. Cancel bake when you start seeing data on screen
10. Check the baked lightmap preview (should look like this https://imgur.com/StFVFda.jpg)
11. Clear Baked Data
12. Shut down editor
13. Start up Editor
14. Bake GI.

Actual result:
The baking stalls.

Workaround is to clear the cache.

The problem is there is no indication of what went wrong and the user will not know how to get out of this situation

Notes:
- Reproduces in: 2019.3f5, 2019.2.18f1, 2020.1.0a18 on Windows
- Could not test in 2019.1 and earlier because of the SRP errors (all geometry is pink)
- When the stall happens, the lightmap has major artifacts (see case 1207755).