I have a wired case, converting polygon geometry to NURBS with a script crashes Maya on a particular object. Printing each step and it looks like a crash is happening on the NURBS step after Poly to Subdiv conversion done.
If I run the conversion piece of code only from Script Editor there are even no errors happening:
string $subdiv_geo[] = `polyToSubdiv -maxPolyCount 100000 -name "SUBD" "polySurface52146"`;
print(">> Poly to SUBD done!\r");
string $nurbs_geo[] = `subdToNurbs -constructionHistory off -name "NURBS" $subdiv_geo[0]`;
print(">> Subd to NURBS done!\r");
Poly to Subdiv is probably sensitive to topology issues that are fine for a polymesh but not reproducible in subd. You might have luck using Maya’s polygon cleanup before the conversion