Equilibrium Iterations (NEQIT)
When using a PolyUMod material model with ANSYS Mechanical you can often get better convergence if you allow ANSYS to use more iterations during the Newton equilibrium search. The screenshot below shows how you can add this using a command snippet.
Stiffness Updates During Contact
Also, when using a PolyUMod material model in contact pair it is often better to allow ANSYS to update the contact stiffness at each iteration (agressively), see screenshot below.