How to reproduce:
1. Open the attached “IN-138559” project
2. Open “OutdoorsScene”
3. Make sure Timeline window/panel is open
4. In the Hierarchy, select “Timeline_Unpack” GameObject
5. Play the timeline, notice playback is smooth
6. Select “Timeline” GameObject
7. Play the timeline
8. Observe the Timeline panel/window
Actual result: Playback is very unresponsive/laggy
Expected result: Playback is responsive, not laggy
Reproducible with: 1.7.1 (2023.1.0a3), 1.8.12 (6000.0.72f1, 6000.6.0a2)
Reproducible on: macOS 26.3 (M1 Pro)
Not reproducible on: No other environments tested
Note: Scrubbing through timeline is also affected