Steps to reproduce

1. Open any existing Unity project (this particular case was tested using the CornellBox project)
2. Navigate to Lighting Settings and make sure that Progressive CPU is set as the lightmapping backend
3. Start the bake
4. Notice as the bake progresses the editor becomes less responsive

Regression introduced in Version 2020.1.0.

Notes:

- Affects both CPU and GPU lightmappers
- Issue does not reproduce if the scene view camera's position is unchanged during the bake
- This issue reproduces both with the Progressive Updates on and off
- Filtering setting does not have any impact
- Reproduces both on Windows and macOS
- Reproduces in: 2020.2.0a13 (542ff463470b), 2020.2.0a12 (a331b04b65b8), 2020.2.0a10 (11fb376d50c9), 2020.2.0a9 (31beeaab9d72), 2020.2.0a8 (8b7e7268f9f8), 2020.1.0b11 (de513167607b)
- Does not reproduce in: 2020.2.0a3 (ba9de6ac812d), 2020.2.0a5 (524e0703ed85), 2020.2.0a7 (cea774d83c47), 2019.4.0f1 (28bf9ffa347b)