Discrepancy between simulation results for S-parameter file

Hi I'm not entirely sure if this should belong in this subforum or one related more to circuit simulation, but here goes.

I simulated a structure in HFSS and was able to export an equivalent *.s4p file so that I could use it in Cadence Virtuoso. However, when I run port analysis in Cadence, the resulting s-parameter simulation is different. I have checked both the single-ended and mixed-mode results, and everything except the SDD21 plot is the same. If anyone has any insight it would be greatly appreciated.

hfss:

Cadence Virtuoso:

Thanks.