Speed trees on terrain are not rendered in prefab editor and assertion failed error spams console

Steps to Repro:
1. Create a new or open attached project
2. Hierarchy > right click
3. 3D Object > terrain
4. drag and drop terrain in the project window to create a prefab
5. Select the prefab and click "Open Prefab" button
6. Select 'Paint Trees' tab > edit tree
7. Add a speed tree
8. Paint trees on the terrain

Actual Result:
1. Painted speed trees the in prefab editor
2. Assertion failed error spams console on painting speed trees

Expected Result:
1. Painted speed trees should be visible in prefab editor

Note:
1. If a game object is added in place of speed tree it is rendered
2. Heightmaps, textures, detail texture and meshes are getting rendered

Environment:
Windows and Mac

Occurring with:
2019.1.0a10, 2018.3.0b11, 2018.3.0a2 (e9113db2e9bf Branch: prefabs/improved)

Stack Trace:
Assertion failed on expression: 'probeSetData.identifier.IsValid()'