Thanks for your patience.
I ran your simulation and I noticed that it stops before triggering auto shutoff. As a result of early shutoff, transmission in port3 has ripples and sometime goes above 1. Since your structure was very large, it takes a long time to finish and I was unable to run it for longer times.
Can you please increase the simulation time and run it until it trigger auto shutoff, and update me with the results.
I was also concerned why you were performing 2D simulations? You can use varFDTD to run 2.5D simulation with a better accuracy compared to 2D and faster than 3D. For a good discussion in this regard please see the links below:
Overall, for large ring resonators, you can simulate half-ring or the coupling sections and sent it INTERCONNECT. This should save you a lot of time. Also, it might be very useful to check how you can calculate coupling coefficient in a ring resonator.
Sorry for bombarding you with the links, I just wanted to give you an overview of the available options
Please let me know of the approach that you are interested in, and I am happy to discuss it further with you.