How to reproduce:
1. Open attached Unity project
2. Select the first object in Hierarchy
3. Hold down the Ctrl button and down arrow key until all objects are selected

Expected result: Scrollbar should follow the last selected item
Actual result: Scrollbar has a delay and catches up only when the last object of hierarchy is selected

Fixed in: 2018.3.0a10

Regression first introduced in: 5.6.0a1
Reproducible with: 2018.1.0b1, 2017.3.0p2, 2017.2.1p2, 2017.1.3f1, 5.6.4p4, 5.6.0a1
Not reproducible with: 5.5.6f1

Note:
It's only reproduced on Windows