I can't pass my programming assignmet auto grading

(the link to the assignment. programming assignment2 and it’s class library are the programming auto grader.
and there is a pdf that tells what to do. TaketheShortWayHome is the game that i have to develop.
I’m only allowed to modify SortedLinkedList.cs , Traveler.cs , GraphBuilder.cs)
i have a programming assignment with unity that asks me to make the player to move from the start node to the end node in the shortest way possible.
I have build the GraphBuilder.cs and most of Traveler.cs(i don’t know what to implement in start method) and SortedLinkedList.cs
but the cases from 6 to 10 always show me “Failed” i don’t know what i should modify in GraphBuilder.cs and Traveler in order to pass all test cases