To reproduce:

1. Download attached project "New Unity Project.zip" and open in Unity
2. Open "SampleScene" scene
3. Put "NewBehaviourScript" script on gameObject in Hierarchy
4. Enter Play mode
5. Observe that Console will print a warning "PlayableGraph being evaluated with no outputs. Playables will not be updated"
6. Exit Play mode
7. Open "NewBehaviourScript", Comment "graph.Destroy();" line and save it
8. Enter Play mode
9. Observe that Console will print a warning "PlayableGraph was not Disposed"

Notes:
- This issue appears on Windows and OSX

Reproduced on Unity 2017.2.3p4, 2017.3.2f1, 2017.4.11f1, 2018.1.9f2, 2018.2.8f1, 2018.3.0b2 and 2019.1.0a1