The Social Security Administration website crashed four times in 10 days this month, blocking millions of retirees and disabled Americans from logging in to their online accounts because the servers were overloaded. In the field, office managers have resorted to answering phones at the front desk as receptionists because so many employees have been pushed out. But the agency no longer has a system to monitor customers’ experience with these services, because that office was eliminated as part of the cost-cutting efforts led by Elon Musk.