CSV fails to import Custom Step Fields

Hello everyone

I am currently trying to import a Helix ALM export (.xml) to Zephyr using a script. The resulting .csv file is correctly formatted and double checked using csvlint.

The problem is the following: I have added custom text fields in the Test Steps section (Step-note, Comment) and these simply get replaced with empty cells or get lost after/during the import, while all other fields are accepted as normal (Name, scope, objective, description, custom boolean fields,  custom integer fields, non-step custom text fields, steps, expected result). I tried it with single-line fields and multi-line.

This is purely conjecture but it's as if it deletes any fields that are not by default part of the Test Execution script, since Comment and Step-note can be added afterward and they appear as normal when the test is reloaded.

Anyone have any idea where the issue could be?