Steps to reproduce:

1. Open the attached "Animation.zip" project
2. Make sure the Animation window is docked and active somewhere in the Editor
3. From the Hierarchy, select the "Cube" GameObject
4. Enter Play mode
5. Observe the Animation window preserves the "Cube" selection and shows animation
6. Exit Play mode
7. Enter Play mode again
8. Observe the Animation window 

Actual results: The Animation window shows "No animatable object selected" despite GameObject being selected 

Expected results: The Animation window preserves the "Cube" selection and shows the animation, exactly as it does the first time entering Play mode.

Reproducible with versions: 2023.1.0b1, 6000.0.71f1, 6000.3.12f1, 6000.4.1f1, 6000.5.0b1, 6000.6.0a1

Tested on (OS): macOS 26.3, Ubuntu 24.04

Notes:

• This issue was partially fixed on 6.5 and 6.6, but it appears the fix only applies to the first time entering Play mode