How to reproduce it:
1. Open the attached project ("Scrollbar Test.zip")
2. Load "SampleScene" Scene
3. In the Hierarchy view select 'Canvas' > 'Scrollbar'
4. Enter Play Mode
5. Click on start and on the end of Scrollbar in the Game view
6. Observe the Value's field in Inspector window > Scrollbar component

Expected result: When clicked on the Scrollbar's start, the Value becomes 0. When clicked on the end, the Value becomes 1
Actual result: When clicked on the Scrollbar's start, the Value becomes nearly 0. When clicked on the end, the Value becomes larger than 1

Reproducible with: 2018.4.32f1, 2019.4.20f1, 2020.2.5f1, 2021.1.0b7, 2021.2.0a5

Notes:
- Repeat 5 and 6 steps (might take from a few to 10 times to reproduce)