diff --git a/lib/connection.js b/lib/connection.js
index 542bdf3c572..05ff52461b0 100644
--- a/lib/connection.js
+++ b/lib/connection.js
@@ -829,6 +829,30 @@ Connection.prototype.openUri = async function openUri(uri, options) {
   return this;
 };
 
+/*!
+ * Treat `on('error')` handlers as handling the initialConnection promise
+ * to avoid uncaught exceptions when using `on('error')`. See gh-14377.
+ */
+
+Connection.prototype.on = function on(event, callback) {
+  if (event === 'error' && this.$initialConnection) {
+    this.$initialConnection.catch(() => {});
+  }
+  return EventEmitter.prototype.on.call(this, event, callback);
+};
+
+/*!
+ * Treat `once('error')` handlers as handling the initialConnection promise
+ * to avoid uncaught exceptions when using `on('error')`. See gh-14377.
+ */
+
+Connection.prototype.once = function on(event, callback) {
+  if (event === 'error' && this.$initialConnection) {
+    this.$initialConnection.catch(() => {});
+  }
+  return EventEmitter.prototype.once.call(this, event, callback);
+};
+
 /*!
  * ignore
  */
diff --git a/lib/helpers/schema/applyWriteConcern.js b/lib/helpers/schema/applyWriteConcern.js
index fcce08f8410..27098110872 100644
--- a/lib/helpers/schema/applyWriteConcern.js
+++ b/lib/helpers/schema/applyWriteConcern.js
@@ -6,6 +6,12 @@ module.exports = function applyWriteConcern(schema, options) {
   if (options.writeConcern != null) {
     return;
   }
+  // Don't apply default write concern to operations in transactions,
+  // because setting write concern on an operation in a transaction is an error
+  // See: https://www.mongodb.com/docs/manual/reference/write-concern/
+  if (options && options.session && options.session.transaction) {
+    return;
+  }
   const writeConcern = get(schema, 'options.writeConcern', {});
   if (Object.keys(writeConcern).length != 0) {
     options.writeConcern = {};
diff --git a/test/connection.test.js b/test/connection.test.js
index 9ea81e356d0..3d1170838cf 100644
--- a/test/connection.test.js
+++ b/test/connection.test.js
@@ -916,6 +916,21 @@ describe('connections:', function() {
     assert.equal(err.name, 'MongooseServerSelectionError');
   });
 
+  it('avoids unhandled error on createConnection() if error handler registered (gh-14377)', async function() {
+    const opts = {
+      serverSelectionTimeoutMS: 100
+    };
+    const uri = 'mongodb://baddomain:27017/test';
+
+    const conn = mongoose.createConnection(uri, opts);
+    await new Promise(resolve => {
+      conn.on('error', err => {
+        assert.equal(err.name, 'MongoServerSelectionError');
+        resolve();
+      });
+    });
+  });
+
   it('`watch()` on a whole collection (gh-8425)', async function() {
     this.timeout(10000);
     if (!process.env.REPLICA_SET) {
diff --git a/test/docs/lean.test.js b/test/docs/lean.test.js
index 4512c7ced7f..e571987864b 100644
--- a/test/docs/lean.test.js
+++ b/test/docs/lean.test.js
@@ -42,7 +42,7 @@ describe('Lean Tutorial', function() {
     const leanDoc = await MyModel.findOne().lean();
 
     v8Serialize(normalDoc).length; // approximately 180
-    v8Serialize(leanDoc).length; // 32, about 5x smaller!
+    v8Serialize(leanDoc).length; // approximately 55, about 3x smaller!
 
     // In case you were wondering, the JSON form of a Mongoose doc is the same
     // as the POJO. This additional memory only affects how much memory your
@@ -50,7 +50,7 @@ describe('Lean Tutorial', function() {
     JSON.stringify(normalDoc).length === JSON.stringify(leanDoc).length; // true
     // acquit:ignore:start
     assert.ok(v8Serialize(normalDoc).length >= 150 && v8Serialize(normalDoc).length <= 200, v8Serialize(normalDoc).length);
-    assert.equal(v8Serialize(leanDoc).length, 32);
+    assert.ok(v8Serialize(leanDoc).length === 55 || v8Serialize(leanDoc).length === 32, v8Serialize(leanDoc).length);
     assert.equal(JSON.stringify(normalDoc).length, JSON.stringify(leanDoc).length);
     // acquit:ignore:end
   });
diff --git a/test/docs/transactions.test.js b/test/docs/transactions.test.js
index 5d0277a5aa4..8b883e3388c 100644
--- a/test/docs/transactions.test.js
+++ b/test/docs/transactions.test.js
@@ -477,4 +477,20 @@ describe('transactions', function() {
 
     assert.equal(i, 3);
   });
+
+  it('doesnt apply schema write concern to transaction operations (gh-11382)', async function() {
+    db.deleteModel(/Test/);
+    const Test = db.model('Test', Schema({ status: String }, { writeConcern: { w: 'majority' } }));
+
+    await Test.createCollection();
+    await Test.deleteMany({});
+
+    const session = await db.startSession();
+
+    await session.withTransaction(async function() {
+      await Test.findOneAndUpdate({}, { name: 'test' }, { session });
+    });
+
+    await session.endSession();
+  });
 });