Hi @swimpark
I have not encountered any problems in saving the checkpoint to .zip as follow for cartpole_train.py using sb3-v1.6.2. Make sure this method is called at some point during the script execution
...
model.learn(total_timesteps=100)
log_dir = "test"
model.save(log_dir + "/jetbot_policy")
Well, in any case, you can always move to another RL library with a higher level (at least for me) of code control such as skrl. I know, I am 100% biased 😅
For question 2, please refer this post, it may help