How to reproduce:
1. Open the attached "Side Bloom" project
2. Open the "SampleScene" Scene
3. Open the Game view window (Window->General->Game)

Expected results: There's no black fading line at the right sides of the Game view display
Actual results: There's a black fading line at the right side of the Game view display

Reproducible with: 5.3.1, 10.0.0-preview.27 (2019.4.10f1, 2020.1.6f1, 2020.2.0b3)
Could not test with: 0.1.21, 5.2.3 (2018.4.27f1, 2019.3.0a11) because the Bloom Override was introduced in the 5.3.1 version which is available in Unity 2019.3.0a1 and above

Notes:
- The issue has been tested and reproduced on Windows 10
- Changing the Game view Aspect from a resolution to an aspect ratio will make a black line appear at the top of the Game view display and the black line at the right will become a transparent straight line instead of a fading black line
- The black lines do no appear in the Build
- The issue is not reproducible with Universal RP and Post Processing packages
- The issue is always visible if the Aspect is set to an aspect ration rather than resolution while the issue is less visible the higher the resolution (at 3840x2160 resolution the issue does not appear at all while at 1366x768 resolution it's still visible)