Key parts of the Social Security website have proven inaccessible over the past week, and the agency now says that it is probing the cause of the service disruptions. The problems come not long after the agency compelled retirees to seek help more exclusively online, as it attempts to downsize its phone operations. Last week, the Washington Post reported that the agency’s website had crashed “four times in 10 days this month because the servers were overloaded, blocking millions of retirees and ...