Users authorized to access particular tasks perspective (Task Administration or Tasks) are not able to see the task list, if the chosen filter tab is expected to show any tasks i.e. the list is not empty.
In this case, Workbench throws an error dialog (screenshot attached). When the error is acknowledged, the page keeps loading indefinitely and the only way to restore control over UI is to refresh the page.
When the process instance, containing the task which supposed to be listed, is aborted, the view of task list is restored.