Repro steps:
1. Create a new VFX or select an existing one
2. Open it in the VFX Window
3. Drag two instances in a new scene.
4. Make sure the scene view is visible
5. Select the first instance of the VFX
6. Observe the VFX controls in the scene view
7. Delete the first VFX instance
8. Observe the VFX controls in the scene view are mostly gone (with a little gray rectangle still visible)
9. Select the other VFX in the scene
10. Observe the VFX controls in the scene view do not reappear.

Notes:
- does not repro in 2019.2.12f1 / 6.9.2
- happens also in 2020.1.0a15 / 8.0.0
- undoing the delete or reopening the project fixes the issue.