Clarity 3D showing significantly higher losses in a coplanar waveguide than ADS for the same structure

When following a Clarity 3D tutorial, which makes a coplanar waveguide, the simulated S-parameters show that it is a very lossy system. I obtain the same results as the tutorial shows, but these results do not make sense to me. It shows an impedance matched waveguide (S11 < -15 dB) with an S21 of -3 dB at 20 GHz for a PCB waveguide of 2.5 mm. The dielectric used is Rogers 4350b with a loss tangent of roughly 0.0037. A loss of over 1 dB per mm seems quite large to me, especially when compared to results from the datasheet of Ro4350b (This shows an insertion loss of < 0.5 dB/inch at 20 GHz) and when performing a simulation in ADS with the same dimensions and materials for the waveguide it also shows a loss of <0.1 dB for a 2.5 mm waveguide.

I tried changing the loss tangent to 0, but this didn't change the loss significantly.

I tried increasing the conductivity to reduce ohmic losses, but this also didn't lead to a significant change.

Also increasing the dielectric constant while keeping the waveguide impedance matched to reduce the radiative losses didn't yield a improvement.

Is someone able to explain if there is a loss which is taken into account in Clarity 3D and not in ADS or whether the loss indeed should be lower.

Thank you in advance

Below are images of the waveguide in Clarity 3D