The ping index is invalid: "ping" : ISODate("1970-01-01T00:00:00.001Z")
configsvr> db.lockpings.getIndexes() [ { "v" : 1, "key" : { "_id" : 1 }, "ns" : "config.lockpings", "name" : "_id_" }, { "v" : 1, "key" : { "ping" : ISODate("1970-01-01T00:00:00.001Z") }, "ns" : "config.lockpings", "name" : "ping_" } ] configsvr>