Agent following path moves forward indefinitely

Question

I am trying to make a sprite move towards a point while avoiding some obstacles. The graph that I am using is a GKObstacleGraph, obtained from this scene:

For simplicity I decided not to use a circular physics body for the obstacles, but it's enough to use the sprites' bounds for now. So this is how I created the graph:

lazy var graph:GKObstacleGraph? =
{
    guard let spaceship = self.spaceship else { return nil }

    let obstacles = SKNode.obstacles(fromNodeBounds: self.rocks)
    let graph = GKObstacleGraph(obstacles: obstacles, bufferRadius: Float(spaceship.size.width))
    return graph
}()

When the user taps on any location of the scene, the spaceship should start moving toward that position by avoiding the obstacles:

func tap(locationInScene location:CGPoint)
{
    guard let graph = self.graph else { return }
    guard let spaceship = self.spaceship else { return }

    let startNode = GKGraphNode2D(point: vector_float2(withPoint: spaceship.position))
    let endNode = GKGraphNode2D(point: vector_float2(withPoint: location))

    graph.connectUsingObstacles(node: startNode)
    graph.connectUsingObstacles(node: endNode)

    let path = graph.findPath(from: startNode, to: endNode)
    print(path)
    let goal = GKGoal(toFollow: GKPath(graphNodes: path, radius: Float(spaceship.size.width)) , maxPredictionTime: 1.0, forward: true)
    let behavior = GKBehavior(goal: goal, weight: 1.0)
    let agent = GKAgent2D()
    agent.behavior = behavior

    graph.remove([startNode, endNode])
    spaceship.entity?.addComponent(agent)

    // This is necessary. I don't know why, but if I don't do that, I 
    // end up having a duplicate entity in my scene's entities array.
    self.entities = [spaceship.entity!]
}

But when I tap on a point on the scene, the spaceship starts moving indefinitely upwards. I tried to print the position of the GKAgent at every frame, and this is what I got:

With very low values, the spaceship still keeps moving upwards without stopping, ever.

This is my project on GitHub.