As described by some previous users, I have the same issue with no pts being assigned to edges, even though they are recognised as having an edge between them.
i.e. for
edge = graph[s][e]
'pts' not in edge = True
I think this is happening between two nodes where there is a small side branch (see skeleton) where if there are no pts attributed with an edge I have just drawn a straight line between start and end coordinates
