I was investigating on why a series of scenes in this project had a dirty state on open scene.
I noticed it was to do with the Canvas objects being in the scene, so I wanted to make the Canvas objects into prefabs to test my theory.
On dragging a second canvas object to the project window to make it a prefab, i got this crash.
========== OUTPUTTING STACK TRACE ==================

0x0000000140ECD4DD (Unity) YAMLScalar::GetStringValue
0x0000000140F8540D (Unity) GetPrefabDynamicDependencies
0x0000000141ED4C2A (Unity) AssetInterface::TakeReadyRefreshAsset
0x0000000141ECA57F (Unity) AssetInterface::ProcessAssetsImplementation
0x0000000141ED4914 (Unity) AssetInterface::StopAssetEditing
0x0000000141EC5B08 (Unity) AssetInterface::ImportAtPath
0x0000000141E83997 (Unity) AssetDatabase::ImportAtPath
0x0000000140E21065 (Unity) SavePrefab
0x000000014121EBD2 (Unity) HandleProjectWindowPrefabDrag
0x000000014122B1B1 (Unity) ProjectWindowDrag
0x000000014128328D (Unity) InternalEditorUtilityBindings::ProjectWindowDrag
0x00000001422BC1A0 (Unity) InternalEditorUtility_CUSTOM_ProjectWindowDrag
0x0000000077E9F287 (Mono JIT Code) (wrapper managed-to-native)

Repro Steps:
1. Download this project
2. When opening it with Unity 2018.3.0a6 --> 2018.3.0b4 or Trunk it will crash

Alternative repro steps:
1. download the Inventory Pro asset
2. Go to Assets\Devdog\InventoryPro\Demos\Scenes\BehaviorDesigner and open that scene
3. Grab the Canvas object and drag it to the Project window to make it a prefab.
4. notice the crash
5. notice that if you try to open the project again, it will crash again -> possible loss of data issue!