When it comes to automation rules that run on ticket creation, the order in which the rules are listed under Admin > Workflows > Automations > Ticket creation tab plays a huge role.
A new incoming ticket will trigger the first rule from the list, with which the conditions are met. Once the ticket satisfies the conditions of one rule, the conditions of the rules listed below will not be checked. Please make sure that the rule that isn't working for you is higher up on the list.
Also, click on 'Activities' on the ticket page to know which rule was executed on the ticket. Based on this, you can reorder the rules under the Ticket creation tab.
Ideally, you should have rules with specific conditions towards the top and the more generic rules lower down in the list.