When configuring an advanced workflow to hide a field when a specific variable is met, the user task cannot be set to Hidden if the task is required.

Making the task required forces task completion. If the task is set to optional, the task can be hidden and skipped when the required variable is met.

For example, if the Review task is not necessary when the country is set to Brazil, the task can be optional and hidden when the country selected is Brazil. Then, the task does not appear.

If the task is set as required and hidden, the task appears even if the country selected is Brazil. The workflow cannot proceed until the task is completed.

Related Documentation:

Vault Help Documentation: About the Workflow Role Setup Object