How to reproduce:
1. Open the project attached by the user (Bugreport2.zip), open the "bug" Scene
2. Select "Pathfinding" in the Hierarchy
3. Observe the incorrect splicing near the "Cube" GameObject
4. Play the Scene, attempt to move the red Agent near the "Cube" GameObject
5. Observe as the Agent's pathfinding is blocked by the incorrect splicing

Expected result: The incorrect splicing does not occur and the Agent can move through
Actual result: Since the splicing is incorrect, the Agent cannot move through

Reproducible with: 2017.1.0a1, 2017.1.4p1, 2017.2.3p1, 2017.4.5f1, 2018.1.4f1, 2018.2.0b8, 2018.3.0a1

Notes: Have not been able to reproduce on my own, it seems that this requires very specific and random placing of GameObjects.