How to reproduce:
1. Create a new project in your preferred workspace and open it
2. Connect it to Perforce and check out 10-20 assets
3. Try to resize the window slowly for the scroll bar to appear/disappear (See Video)
4. Observe that at certain sizes the scroll bar disappears even though there are still assets in the list that are not visible

Expected result: The scroll bar is always present when there are assets in the Window that are not visible
Actual result: At certain sizes, the scroll bar disappears even though there are assets that are not visible

Reproduced in: 2020.1.0a7, 2019.3.0b5, 2019.2.7f2, 2018.4.10f1, 2017.4.32f1

Note: Windows like the Inspector do not seem to have this issue, tried it with most asset types like Materials/Scripts/Audio Mixers etc.