The following test reproduces this issue: (function() { "use strict";   const dbName = "applyOpsReplicatedCreateIndexCrash"; const collName = "coll";   const rst = new ReplSetTest({nodes: 2}); rst.startSet(); rst.initiate(); const db = rst.getPrimary().getDB(dbName); const coll = db.getCollection(collName);   db.coll.drop(); db.coll.insert({}); db.adminCommand({ applyOps: [{ op: 'c', ns: coll.getFullName(), o: { createIndexes: coll.getName(), v: 2, background: {a: 1}, name: 'a_1_create_v2', unknown: 1 } }] });   rst.stopSet(); })();