StableBaselines-3 DDPG + HER Multiprocessing

I was reading documentation about HER and also about Multiprocessing in stable-baselines3 website However when i try to train it throws a error! Is there any example anywhere with multiprocessing with replay_buffer??

num_cpu = 4
env = make_vec_env(env_name, n_envs=num_cpu, seed=0, vec_env_cls=SubprocVecEnv)
model = DDPG(
    'MultiInputPolicy',
    env,
    verbose = 1,
    tensorboard_log = log_path,
    replay_buffer_class = HerReplayBuffer,
    # Parameters for HER
    replay_buffer_kwargs=dict(
        n_sampled_goal = 4,
        goal_selection_strategy = GoalSelectionStrategy.FUTURE,
        online_sampling = True,
    ),
)
model.learn(total_timesteps = 1000000)

ValueError: could not broadcast input array from shape (6,4) into shape (4,)