Possible physical compromise. Does he live with a room mate? Did he left his phone somewhere? Malware on phone?

They are all quite unlikely, but then again reports of 2FA hacks are very very rare.

老外的回复。

是否有可能是你的手机被盗用过或者谁使用过你的手机而且有动机盗窃。检查一下你的手机上有没有木马软件。