Might be a small detail, but each time you are testing the automation, are you just testing the automation action to see if it works? Or are you starting the entire automation test beginning from the trigger?
If you create an automation, test the trigger, and start testing an action, even if the original record in the table is changed, the data being tested in the automation is like a snapshot of the record that triggered the automation.
So if you update the record’s Owner field and just go to test the action, nothing will be different because you haven’t loaded a new “snapshot” or payload of test data for the automation.
It’s a bit weird to explain, so please let me know if you need any additional clarifying information on it.