How to reproduce:
1. Open the “TestTimeline” project
2. Open the “ReproScene”
3. Double-click on “New Timeline” asset to open it in the Timeline window
4. Lock the Timeline window
5. Enter Play Mode
6. Click on the Visual Effect Control Track’s clip
7. In the Inspector change any value of Attribute (ex. increase the “Size” value)
8. Exit Play Mode
9. Repeat steps 5-8
10. Observe the Console

Expected result: No errors are thrown in the Console
Actual result: Numerous “NullReferenceException” errors are displayed

Reproducible with: 6000.0.54f1
Could not test with: 2022.3.65f1, 6000.1.13f1, 6000.3.0a3 (Reproduction is inconsistent)

Reproducible on: Windows 10
Not reproducible on: No other environments tested

Notes:
- Only managed to reproduce the issue once with version 6000.0.54f1
- Couldn’t reproduce the issue after re-opening the project
- Couldn’t reproduce the issue on any new project