Scenario1
Steps:
1. Open attached project (works with a new project too)
2. Open SampleScene
3. Select one of the GameObjects in the Hierarchy
4. Drag it through the Hierarchy without releasing
==>
At some point some random GameObject will be moved while you still performaing a drag

Scenario2
Steps:
1. Open attached project (works with a new project too)
2. Open SampleScene
3. Drag any GameObject to another position in Hierarchy
4. Select another GameObject
5. Drag it to the Scene view (without releasing the left mouse button)
6. Go back to the Hierarchy (still in a drag mode)
==>
Selection changes to the first dragged object

Also repro in: 2020.1.0b5, 2019.4.11f1, 2018.4.22f1, 2021.1.0a1