To move a Next Gen project to a Classic you must export your data and then import it into a new Classic project. I have done this multiple times today and each time am unsuccessful on some level. I've reached my breaking point and am reaching out for help. During my import I am losing all the children that are associated to an Epic. I have ensured the fields are visible on the new board and I have named and mapped them in the CSV and the fields during import. However, every time I import I lose the parent/child association between an Epic and its tasks.