After I knew the working principle of the workflow, I adjusted my workflow. I created several workflows separately, and each workflow they are used for users in different states, such as 'sign up', 'free account', 'paying account'.
I tested based on this, manually creating a new user, so he received the email set in 'sign up' two seconds after creation. After a while, I manually changed its status to 'free account' and it didn't receive the email for the second workflow setup. Then manually change its status to 'paying account', but still haven't received the email set by the third workflow. What's going on here, I think my logic is set very simply, just after the user's status changes, and then send him a corresponding email.
I want to make sure if it's something wrong with my logic setup (which is fixable) and not the customer.io tool itself.