Thanks for that. Do you have any links to reports about Graphviz crashes with similar messages? That could be very helpful.

Most of my graphs are pretty small (less than ten nodes). And which one fails seems to be random, and more importantly, it works perfectly and is not unusual when it is retried. So I don't think it is a data-dependent Graphviz error. The dot files look sensible.

FWIW, here's where I mess with Graphviz

    $self->{graph} = GraphViz2->new(
                    global  => {
                        name    => 'fold_graph_map',
                    },
                    node    => {
                        fontsize => 10,
                        shape    => 'box',
                    },
                );

stuff adding nodes and edges omitted

    eval {
        $self->{graph}->run(format  => 'png');
        $png   = $self->{graph}->dot_output();
    };
    die "Failed to create png for node #$id:\n$@\n"
        . $self->{graph}->dot_input()
      if $@;