Pipeline not updating the reference field

I need the data from A table to B table. So I created a relation between them with X Field as reference field which is not unique field. I am having 5 lookup fields from parent to child.
The workflow is in such a way that fields respect to parent table record create a new record when updated. But as the reference field is same for both records the pipeline is not making the change in the child table and look ups are not getting updated due to this