The <adf-task-header> component will display a Requeue button for assigned tasks (i.e. they are not candidate tasks/pooled tasks), which means that they can't be requeued, meaning there is no pool to put the task back in.
More detail of the background of the issue
When you define a User Task (Activity) you need to set how it is going to be assigned to somebody. You can assign directly to a user, or you can assign to a group of people (candidate task, pooled task), which means that someone in the group needs to claim the task before working on it, meaning it will disappear from the pool and from other users task list. However, sometimes after a user has claimed a pooled task they might get other things to do and they want to put it back in the pool so another user in the group can claim it and work on it instead. Putting the task back in the pool is called Requeue in our app. But when using the <adf-task-header> the Requeue button is displayed also for directly assigned tasks.
Basically, if you are looking at a task via <adf-task-header> and it is directly assigned to a user there should be no Claim or Requeue button. If it is a pooled task, then it should show a Claim button if it is still in the pool, and a Requeue button if the user has claimed the task.