The load_user() funtion not being called after login_user(user) is called in flask-login

Question

I am using MongoEngine to save userid(primary key), username, role, and password. I have used flask-login. Even after running login_user(user) successfully, the control isn't going inside the function load_user().

This is my User model:

db = MongoEngine()

class User(db.Document, UserMixin):
    username = db.StringField(required=True)
    role = db.StringField(required=True)
    request_pending = db.BooleanField(required=True)

    class Meta:
        indexes = [
            {
                'fields': [('username', 1), ('role', 1)],
                'unique': True,
            }
        ]

    password_hash = db.StringField(required=True)

    def check_password(self, password):
        return check_password_hash(self.password_hash, password)
    
    def set_password(self, password):
        self.password_hash = generate_password_hash(password)

This is my login() function:

@app.route('/api/login', methods=['POST'])
def login():
    print("Login Requested")
    data = request.json
    username = data.get('username')
    password = data.get('password')
    role = data.get('role')

    # check if username+role exists
    user = User.objects.filter(username=username, role=role).first()
    if user and user.request_pending == False and user.check_password(password):
        login_user(user)
        session['username'] = username
        session['role'] = role
        return jsonify({'message': 'User logged in successfully', 'user': username, 'role': role}), 201
    elif user and user.request_pending == True:
        return jsonify({'error': 'Registration not approved yet'}), 401
    else:
        return jsonify({'error': 'Invalid username or password'}), 401

This is my logout() function:

@app.route('/api/logout', methods=['POST'])
@login_required
def logout():
    logout_user()
    session.pop('username', None)
    session.pop('role', None)
    return jsonify({'message': 'Logged out successfully'}), 201

This is my load_user() function along with the initialisation:

app = Flask(__name__)
app.secret_key = secrets.token_hex(16)
CORS(app, supports_credentials=True)
app.config['MONGODB_SETTINGS'] = {
    'host': '<my mongo atlas host>'
}
db.init_app(app)

# set up Flask-Login
login_manager = LoginManager()
login_manager.init_app(app)

# user loader function
@login_manager.user_loader
def load_user(id):
    try:
        print("Was here 1")
        return User.objects.get(_id=id)
    except:
        print("Was here 2")
        return None

When I call login() and logout() respectively, 2 problems:

1. Neither Was here 1, nor Was here 2 gets printed indicating that load_user is not called.
2. Even after successful login, logout gives 401 error i.e. login_required is not letting control go inside logout()

Output:

10.2.138.51 - - [09/May/2023 13:08:49] "OPTIONS /api/login HTTP/1.1" 200 -
Login Requested
10.2.138.51 - - [09/May/2023 13:08:50] "POST /api/login HTTP/1.1" 201 -
10.2.138.51 - - [09/May/2023 13:08:51] "OPTIONS /api/logout HTTP/1.1" 200 -
10.2.138.51 - - [09/May/2023 13:08:51] "POST /api/logout HTTP/1.1" 401 -

My frontend is on a remote machine with cookies enabled in its browser. I tried turning the debug mode on and off, I also tried passing remember=True to login_user(), but nothing seems to be working. Please help.