Reproduction steps:
1. Create a new HDRP template project
2. Make sure Scene and Game windows are docked in the same tab
3. In the Game window, add a new 640x360 resolution and select it
4. In the top right corner of the Game window, enable Stats
5. Enter Play Mode and observe the framerate
6. Switch to the Scene window and then back to the Game window
7. Observe framerate

Expected result: Framerate before and after switching to the Scene window is the same
Actual result: Framerate after switching to the Scene window is around twice as high (increases from around 10FPS to around 25FPS in most cases)

Reproducible with: 10.2.2 (2020.2.0b12), 12.0.0 (2021.2.0a7)
Not reproducible with: 10.1.0 (2020.2.0b12)
Could not test with: 10.2.0, 10.2.1 (2020.2.0b12, the project would either freeze or cause a kernel panic, most likely caused by case 1291998)

Reproduced with:
1,6 GHz Dual-Core Intel Core i5, Intel UHD Graphics 617 1536 MB, MacBook Air (Retina, 13-inch, 2019)
2,7 GHz Quad-Core Intel Core i7, Intel Iris Plus Graphics 655 1536 MB, MacBook Pro (13-inch, 2018, Four Thunderbolt 3 Ports)

Could not reproduce:
4.2 Ghz Quad-Core Intel Core I7, Radeon Pro 580 8 GB, iMac (Retina 5K, 27-inch, 2017)
Intel(R) Core(TM) i7-8850H CPU @ 2.60GHz, NVIDIA GeForce GTX 1050Ti, Windows 10

Note:
- Not reproducible when using Free Aspect or higher resolutions
- Not reproducible with URP