Steps to repro:

1. Pull the Sponza URP project: https://ono.unity3d.com/test-data/gi-tests/SponzaLWRP and update to the revision f9dd3efa4fae9b3552d61d921c3894f433fecd35;
2. Open SponzaLightingDay scene;
3. Pull the Sponza scene to the Hierarchy;
4. Make sure that the scene is selected as a master scene, if not, double-click on SponzaLightingDay scene in the Hierarchy;
5. Make sure that GPU Lightmapper is selected as a baking backend for the SponzaLightingDay scene;
6. In the Lighting window press Generate Lighting button;
7. Once the ETA is visible in the Background Tasks window, in the Lighting windows press Force Stop button and then Cancel button;
8. Press 'Generate Lighting' button again.

Expected result:
Baking finishes without errors.

Actual result:
Baking stalls in the neverending loop. See the attached video.

Notes:
- Reproducible in Version 2021.1.0a6, 2020.2.0b12, 2020.1.14f1;
- Not reproducible in previous versions, since the Force Stop button wasn't working in those;
- Reproducible on Windows with NVIDIA GeForce RTX 2080 GPU and on OSX 10.15.7 with AMD Radeon Pro 560 GPU;
- Workaround is to stop the bake, clear the lighting data and restart the bake;
- Could not reproduce the issue with the CPU Lightmapper;

- The issue might not repro consistently. If it doesn't try following:
- Try repeating steps 6-7 several times in a row with the different delay intervals between pressing Force Stop and Cancel button;
- Restart Editor, clear lighting data and repeat initial steps to repro once again.