To reproduce:

1. Open Unity, create a new project and open it
2. Download attached script "UnityEventCountTest.cs" and attach it to project
3. Attach "UnityEventCountTest.cs" Script to any gameObject
4. Enter Play mode
Note: Observe that the GetPersisentEventCount() returns zero always leaving multiple API's unusable
5. Exit Play mode
6. Go to the Unity Event Documentation
7. Copy that Code which is in the Documentation
8. Go back to your Unity project, create a new script, paste that code from Documentation, paste this snippet
"Debug.Log(m_MyEvent.GetPersistentEventCount());", save a script and attach it to any gameObject
9. Enter Play mode
Note: Observe that it returns zero even though the Unity Event Documentation registers a listener

Notes:
- This issue appears on Windows and OSX

Reproduced on Unity 5.5.5p1, 5.6.4p1, 2017.1.2p2, 2017.2.0p1, 2017.3.0b7 and 2018.1.0a2