Hi,
I understand that you are attempting to submit repeating values using a MSLB control. When mapping a repeating field, you mast select this field as the repeating group, and instead of selecting the field when mapping to your list, enter a dot (.) for the value. It should look similar to this:

And if you are receiving blank values, add a condition such as [. != ""] to filter out blank data.
Please let me know if this helps.