What issue remains when a narrator says “a trustworthy person informed me” but leaves the person unnamed?

Narrator Anonymity: Wuḥdān, Mubham, Majhūl al-ʿAyn and Mastūr

• A break is invariably proven
• The individual remains unidentified and cannot be independently evaluated
• The matn is necessarily fabricated
• The teacher’s chronology is thereby established