In case anyone is following the video verbatim, note that when Ben “fixed” the error around 11m30s, he inadvertently swapped the order of adding the path element and getting the next waypoint, which means the final block in the path (right by the player’s base) is not actually added to the path.
So this:
previous = previous.exploredFrom;
SetAsPath(previous);
Should be this:
SetAsPath(previous);
previous = previous.exploredFrom;
Maybe this gets fixed later.