Oh sh** this is embarrassing :lol: Now it works!

Question type = short free text; default answer is {TOKEN:ATTRIBUTE_1}; always hide this question = yes
-> also saves the default answer to the response & statistics.

Hide it with a question class "hidden ", not with the question setting.

Are are talking about this: edit question > "Advanced settings" tab > "Always hide this question" slider ?
I don't find a question type with "hidden" in its name and you're not referring to CSS classes, right?

Leave the question type as-is, disable "Always hide this question" and add a CSS class.