How to reproduce:
1. Open the "Testninja_wip.zip" project
2. Open the "samplescene_ninja" scene
3. Select "NinjaCharacter4.fbx" in the Project
4. Drag "NinjaCharacter4.fbx" to the Scene view
5. In the Inspector mark "NinjaCharacter4.fbx" as static
6. Select "NinjaCharacter4.fbx" in the Project
7. In the Inspector open the Rig tab
8. Press "Configure" under avatar definition
9. If Unity didn't crash, press "Done" and repeat steps 5-8.

Actual result: Unity crashes. (gif attached)

Reproducible with: 2018.3.0a2, 2018.2.0b9, 2018.2.0a1.
Regression introduced in: 2018.2.0a1.
Not reproducible with: 2018.1.6f1, 2017.4.6f1.

Notes:
It looks like when trying to configure humanoid avatar while lightning is being baked causes this crash.
In 2018.1, sometimes errors appears:
- Assertion failed: Assertion failed on expression: 'm_NumInstanceTransforms == m_NumInstanceLODGroups'
- Assertion failed: Assertion failed on expression: 'm_NumInstanceTransforms == m_NumInstanceLODMasks'
- Assertion failed on expression: 'm_NumInstanceTransforms == m_Instances.size()' (May be irrelevant)
- The crash happened after 10-20 times reloading the scene by entering and exiting avatar configuration during 'Preparing Bake...' stage.
- Following errors are shown during the crash:

OpenRL reported error code 502: OpenRL error occured

in function rlMapBuffer: RL_INVALID_OPERATION: No buffer bound to specified target
(Filename: C:\buildslave\unity\build\Editor/Src/GI/Progressive/PVRContextManager.cpp Line: 87)
and

OpenRL reported error code 502: OpenRL error occured in function rlMapBuffer: RL_INVALID_OPERATION: No buffer bound to specified target