CST - Frequency Domain Solver (TET) Terminated Abnormally

Hi,
I'm modeling an infinite connected slot array with some example stratifications and am running into this error.
The error only occurs when a Farfield Monitor is present. Adding the monitor to an already completed simulation and running again makes it give the same error.
The error occurs for scanning to theta 60 phi 90 (Boundary.SetPeriodicBoundaryAngles "60", "90"), but not for 0, 0 or for 60, 0.

Since I cannot upload my .cst file, and uploading it to a file-sharing website makes Chrome give a "Danger" warning, I have added my parameters and a schematic of the structure. I have also attached the contents of my model.mod.


Constructing the same project in CST 2018 and CST 2020 yields the same error.

My question is: Is there something I can do to circumvent this error, or is it an issue in CST?

Thank you,
Alexander

CST Studio Suite ​​​​​​​

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