Guilin Sun
Ansys Employee

I guess one of the main issue is the output mode:

as you can see, when you use PML, the field profile is similar to sym-ymin. In this case you will need to choose the output mode with y-symmetry property.

As  you can see, the mode profiles agree. So it is the mode issue. If you are not sure the polarization of the mode, you can choose several output modes. Or you can use "user select" to choose proper output mode.

Please note that, when no symmetry BC is used, the effective number of modes is roughly decreased to half of the case with symmetry BCs, since in general odd/even modes cannot be coupled to even/odd modes. When symmtry BC is used, the other half of modes without this symmetry will not appear. I assume roughly odd and even modes are half-half by numbers.