For your first question, you will need to increase the number of the trial modes. By default it is 20. When PML BCs are used, it will create a lot of PML modes, which needs to be get rid off. So more number of modes are required.
It seems it can find modes for larger bending radius, so you will need more number of trial modes in order to find the modes with smaller bending radius, as the mode confinement is weak.
As for the second question, you may need to increase the simulation span, or increase that side where the mode shifts. If you have further questions regarding this, please write another post.
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