Dropped write during insert loop with retry_writes on

1. Start a MongoDB 3.6.2 replica set with FCV 3.6 2. Start a loop in the mongo shell to insert 10,000 documents with retry_writes set to true: use test db = db.getMongo().startSession({retry_writes: true}).getDatabase(db.getName()); for (i = 0; i < 10000; i++) { db.test.insert({}); } 3. While the inserts are happening issue an rs.stepDown() command on the primary 4. The insert loop will eventually finish but db.test.count() will indicate that only 9,999 documents have been inserted.