Repro:
1. Create an animation for an object
2. Dock the Animation Window to left top part of the editor
3. Middle click and pan the time frame to the right, beyond the last keyframe
4. Deselect the animated object in the hierarchy
5. Decrease the size of the whole editor, until AW is totally squeezed.
6. May have to repeat a couple of times, but the AW breaks, and the keyframes, time line are not visible. Selecting the object again doesn't help
Closing and reopening the window fixes it.