Coroutine Freezes Editor with "Out of memory" Error

I am using a coroutine to break up a path finding algorithm (A*) I am using. The algorithm runs fine when not in a coroutine. The function is:

 private IEnumerator C_CreatePath(PathVert startVert, PathVert endVert)
 {
         float startTime = Time.time;
         List<PathVert> open = new List<PathVert>();
         List<PathVert> closed = new List<PathVert>();
         open.Add(startVert);
         
         //Set deafult values before starting algorithm
         for (int row = 0; row < verts.GetLength(0); row++)
         {
             for (int col = 0; col < verts.GetLength(1); col++)
             {
                 PathVert vert = verts[row, col];
                 vert.gCost = int.MaxValue;
                 vert.CalcFCost();
                 vert.parentVert = null;
             }
         }
         startVert.gCost = 0;
         startVert.hCost = CalcDistanceCost(startVert, endVert);
         startVert.CalcFCost();
 
         while (open.Count > 0)
         {
             PathVert currVert =  GetLowestFCostVert(open);
             if (!currVert.isWalkable){ continue; }
             if (currVert == endVert)
             {
                 List<PathVert> vertList = CalcPath(endVert);
                 path = new Path(vertList);
             isDone = true;
             break;
             }
             open.Remove(currVert);
             closed.Add(currVert);
             List<PathVert> neighbors = GetVertNeighbors(currVert);
             foreach (PathVert neighbor in neighbors)
             {
                 if (closed.Contains(neighbor) || !neighbor.isWalkable){ continue; }
                 int tentativeGCost = currVert.gCost + CalcDistanceCost(currVert, neighbor);
                 if (tentativeGCost < neighbor.gCost)
                 {
                     neighbor.parentVert = currVert;
                     neighbor.gCost = tentativeGCost;
                     neighbor.hCost = CalcDistanceCost(neighbor, endVert);
                     neighbor.CalcFCost();
 
                     if (!open.Contains(neighbor)){
                         open.Add(neighbor);
                     }
                 }
             }
         yield return null;
         }
 }