Guilin Sun
Ansys Employee

The dB scale amplifies the ripple. Seldomly EME result shows ripples. I guess you used the "wavelength sweep" utility, which simplifies the sweep with only wavelength change but not the neff and mode profile. To verify, you can also simulate the shortest and longest wavelengths and compare with the sweep result. Usually the initial simulation uses the center wavelength.

Please check the linear scale first.

You may need to compare the settings with the online example and check the differences and reasons. With very limited information it is hard to know the exact causes.