There are 2 overlapping NavMeshes that are part of some geometry instantiated using Prefabs at runtime.
The exception happened after the NPC successfully moved to the player & stopped. Then, occasionally when the player moved, the exception would be thrown. It seems a new path was being calculated, but somehow the Path array indexing got messed up. I can only guess since I can’t step the code.
The “IsPlayerOnGraph” node wasn’t having any effect in this test. Even when I replaced it with a timer (to drop out the parallel), the exception would sometimes be raised.
I’ve replaced the AI.Navigator with a test one (by subclassing the BasicNavigator) so as to try and catch the exception. But I have not seen it since I made that modification.
I’ll let you know if I collect any more information regarding the exception.