How to reproduce:
1. Create new project
2. Import the "Timeline_Package.unitypackage" package
3. Open the "ReproScene" (already takes some time to load)
4. Open Timeline window (Window > Sequencing > Timeline)
5. Select "PARENT MOVE > --- TIMELINES --- > tln_ep201_200_seq030" in the Hierarchy
6. In the timeline window, expand the "Audio" tab
7. Select any sound track and try to move it around

Actual result: The timeline elements starts lagging while being dragged.
Expected result: The timeline elements dragging doesn't start lagging.

Reproducible with: 2020.1.0a23 (1.2.11), 2019.3.0f6, 2019.2.20f1 (1.1.0).

Notes:
- error sometimes is thrown when the elements start lagging:
The script class couldn't be found
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)
- Can't test 2018.4 as the timelines breaks.
- The lags are not reproducible if the timeline object is not selected in the Hierarchy.