I was trying to simulate a photonic crystal based wave-guide bend. Although, the simulation results was OK for a pure periodic structure, it diverges for the wave-guide bend. I have tried with adaptive mesh refinement option and by reducing the stability factor to 0.1. But no improvement was observed.
i dont have solution for your problem because i have never done photonic crystal simulation before. you can try to do below changes to see if you get the results you want.
1) change discrete port to phase port if phase port works for your design.
This seems to indicate that port and boundary are too close together. Changing to open (add space) should increase the distance. I could be wrong, but it seems like if the port is too close to the boundary (or assuming at the boundary), could cause some field issues with reflections from boundary, therefore ensuring that distance of at least three mesh steps is achieved.