Frame rate drops when using multiple monitors with duplicated screen

How to reproduce:
1. Open the attached project "1253558.zip"
2. Open the "Test" Scene
3. Build and Run the project
4. Set your operating system display mode to duplicate (for Windows go to Settings > System > Display and set Multiple Displays to "Duplicate these displays")

Expected result: the frame rate does not drop
Actual result: the frame rate drops below 60fps

Reproducible with: 2019.1.0a10, 2019.4.0f1, 2020.1.0b12, 2020.2.0a14
Not reproducible with: 2018.4.23f1, 2019.1.0a9

Note:

• frame rate drops from an over thousand to less than 60fps
• only reproduces when using multiple monitors with a "Duplicate these displays" mode (for Windows go to Settings > System > Display and set Multiple Displays to "Duplicate these displays")
• only reproduces when Fullscreen Mode is set to "Maximized Window" or "Fullscreen window" (Project Settings > Player > Resolution and Presentation)
• only reproduces with Direct3D11 and Direct3D12 (tested but did not reproduce with Vulkan, OpenGLCore, OpenGLES2, OpenGLES3)
• reproduces with Builtin RP, HDRP, and URP
• does not reproduce if any type of overlay is present (as an example overlay created by screen recording software, windows game bar, Nvidia GeForce experience, etc.)