Hi Matteo, from what I see your playbook only has one "manual task", if I remember correctly the manual task needs to be check as completed by a person to be considered done.
In other words the playbook it's waiting for someone to see the task, read the instructions and execute what needs to be executed manually and then check saying "I've done it", then the playbook will continue their process.
If you want to automatically close tasks then you'll need to use something like Custom Tasks and this app:
https://ibmresilient.github.io/resilient-community-apps/fn_task_utils/README.html
Best regards