Dear Sir or Madam,
It seems that the number of modes from left and right are not equal while using the second nearest hopping. It should work for the first neighbor hopping but not further.
You might overcome this issue by averting the use of a1 and a2 directions. You would simply add the following
sym0.add_site_family(graphene.sublattices[0], other_vectors=[(-1, 2)])
sym0.add_site_family(graphene.sublattices[1], other_vectors=[(-1, 2)])
sym1.add_site_family(graphene.sublattices[0], other_vectors=[(-1, 2)])
sym1.add_site_family(graphene.sublattices[1], other_vectors=[(-1, 2)])
dum_sym.add_site_family(graphene.sublattices[0], other_vectors=[(-1, 2)])
dum_sym.add_site_family(graphene.sublattices[1], other_vectors=[(-1, 2)])
I hope this will fix your issue.
Best wishes
Adel