1. Start a sharded cluster, e.g. with mlaunch init --replicaset --sharded 1 --nodes 3 --mongos 1 2. Kill one of the secondary nodes, e.g. using rs.status() to find a secondary and ps / kill -9 to find the PID and terminate it 3. Run the provided reproduction script for Node and/or Python This should produce the following error from the server on the next find operation: Encountered non-retryable error during query :: caused by :: Incompatible wire version Node repro script 'use strict' ; const MongoClient = require( 'mongodb' ).MongoClient; const uri = 'mongodb: //localhost:27017/?readPreference=secondary&maxStalenessSeconds=90' ; const client = new MongoClient(uri); async function run() { try { await client.connect(); const database = client.db( 'test' ); const collection = database.collection( 'bar' ); for (let i = 0; i < 10000; i++) { const doc = { a: 42 + i }; console.log(await collection.insertOne(doc)); console.log(await collection.findOne(doc)); } } catch (err) { console.error(err); } finally { await client.close(); } } run(). catch (console.dir); Python repro script from pymongo import MongoClient import pprint client = MongoClient( 'mongodb://localhost:27017/?readPreference=secondary&maxStalenessSeconds=90' ) db = client.test coll = db.collection.bar i = 0 while i < 10000: doc = { 'a' : 42 + i } pprint.pprint(coll.insert_one(doc)) pprint.pprint(coll.find_one(doc)) i += 1