It seems that you didn't use actor_target at all

[Triple-ROCK]

in the 233 line of the file ddpg_vec.py, you use
next_action_batch = self.select_action( next_state_batch.view(-1, self.obs_dim), action_noise=self.train_noise),

that means you select next_action use current actor instead of the target actor, which is different from the ddpg paper, or you do this design choice for some other reason?