CNOT Benchmark demo broken: TypeError: Graph doesn't seem circuit like: multiple parents

[balopat]

Running the CNOT Benchmark example under demos fails with

Circuit              qubits G-count 2-count G-NRSCM 2-NRSCM  G-Tpar 2-Tpar G-PyZX 2-PyZX Time-Simp Time-Opt
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-16-fa5aee888fdf> in <module>
      1 print("Circuit".ljust(20), "qubits", "G-count", "2-count", "G-NRSCM", "2-NRSCM", " G-Tpar", "2-Tpar", "G-PyZX", "2-PyZX", "Time-Simp", "Time-Opt")
      2 for c in fast_circuits:
----> 3     print(c.get_output())

<ipython-input-14-eb2f95ae4779> in get_output(self)
     54     def get_output(self):
     55         if not self.has_run:
---> 56             self.run()
     57         s = self.name.ljust(20) + str(self.qubits).rjust(7)
     58         s += " | " + str(self.gatecount).rjust(5) + str(self.cnotcount).rjust(6) + " | "

<ipython-input-14-eb2f95ae4779> in run(self)
     43         self.time_simpl = time.time() - t
     44         t = time.time()
---> 45         c = zx.Circuit.from_graph(g).split_phase_gates()
     46         c = zx.optimize.basic_optimization(c).to_basic_gates().split_phase_gates()
     47         self.circuit_opt = c

~/dev/proj/pyzx/pyzx/circuit.py in from_graph(g, split_phases)
     82                 neigh = [w for w in g.neighbours(v) if rs[w]<r]
     83                 if len(neigh) != 1:
---> 84                     raise TypeError("Graph doesn't seem circuit like: multiple parents")
     85                 n = neigh[0]
     86                 if qs[n] != q:

TypeError: Graph doesn't seem circuit like: multiple parents