Hello,
Apparently, in my project, the rendering of gizmos works well only in the Editor when the Play Mode is not enabled.
I can see the gizmos in SceneView and Game View.

I am using Unity 2018.4.23f1 and the legacy render pipeline (no Render Pipeline Asset).
When debugging, I can see I go through all the drawing process, so I am not sure what is different in Play Mode.
The Gizmos Draw methods are called into my OnRenderObject() method (ExecuteAlways attribute is used to see the result in the editor).

I thought it could come from the onPostRender event, but even without PostProcess activated in the scene, I am not able to see it.

Any ideas ?
Thank you.

EDIT :

After more investigation, it seems the GizmosInstance.queuIndex is equal to 1 when it arrives at OnRendered(Camera cam).
So only the dummy Gizmos is processed. But in the queue, there are all the submitted Gizmos through OnRenderObject()...

I will let you know if I find something.