Millions of people are overdue on their federal loans or still have them paused — and court rulings keep upending collection efforts. At the end of March, six months after the hiatus ended, nearly 20 million borrowers were making their payments as scheduled. But almost 19 million were not, leaving their accounts delinquent, in default or still on pause, according to the latest Education Department data. “The nonpayment rate really is emblematic of a system that’s not doing its job,” said Persis Yu, the managing counsel for the Student Borrower Protection Center, an advocacy group.