Thank you for reaching out to us. As always, without code we cannot do much here. I must also point out that what you are here effectively asking for, us debugging your code for you, is out of scope support. Because you demonstrate yourself that parameters of type FieldList work in principle. To increase your chances of us helping you with debugging, you must minimize your code example (you did not do that in your last case for example and I did it there for you).

Out of my head, reasons for this could be incorrect Get/SetDParameter or TranslateDescID implementations, but that is only a guess and therefore pretty meaningless.

Cheers,
Ferdinand