Hello odoo community

In our helpdesk there must not be a ticket without an activity.

So I created an automated rule with XStudio that creates an activity for every new helpdesk ticket: 

That works wonderfully.

Since this activity can be canceled or deleted, I have created a second automatic rule that checks when updating whether no activity has been set for an open ticket:

This second rule is never executed.

The odoo support said I would have to set up a cron job (Server - Scheduled Actions) for this second rule, which regularly checks whether there are open helpdesk tickets without a set activity and then sets an activity again accordingly.

Since I've never done anything like this and haven't found any help either, I need your help to solve my problem. We have odoo v15 running on odoo.sh. 

Thanks in advance

Gerold