I am also getting crashes to do with scene loading! It would appear that the curvy segments are being destroyed before they get moved into the singleton (perhaps due to Unity's never-ending update order problems). Then, when the pool attempts to remove excess segments (which in fact have already been destroyed), it gets exceptions
The simple solution, I expect, is to null-check the collection of pooled segments before manipulating it.
The simple solution, I expect, is to null-check the collection of pooled segments before manipulating it.