Error message when building a 3D-model

Dear community,

I've expanded the built-in optical ring resonator model from 2D to 3D. Additionally, I've added the same geometry above the model to simulate air and under the model to simulate a substrate (with n = n_clad). Apart from these changes, I've strictly sticked to the definitions etc. as given in the PDF.

Surprisingly, whenever I try to do the parametric sweep (or any other computation), I get the following message:

"Error in sweep. The following feature has encountered a problem:

Internal error in solutionMerge
Variables property does not include all variables in xmesh
-Feature: Dependent Variables 1 (sol1/v1)"

I wonder if this error message has anything to do with me adding a third dimension or if it's maybe that the phase angle is not properly defined with respect to z?

Anyways, I would be happy about any feedback and/or help.

Thanks!

P.S.: Also, please find the model attached.