Steps to reproduce:

1. Open any existing HDRP project
2. In the scene view, switch to Shaded Wireframe mode
3. Move around in the viewport
4. Notice how the wireframe flickers, and sometimes does not get cleared

Notes:

- Only affects HDRP; other render pipelines are not affected
- Only affects Shaded Wireframe view mode; Wireframe mode is not affected
- Observed in 2020.2.0b6 using a MacBook Pro running macOS 10.15.7
- Reproduces in Unity version 2020.2.0b5, 2021.1.0a2
- Reproduces in HDRP version 10.0.0, 10.1.0, 11.0.0