What is the ruling on the prayer of a congregant when the voice of the Imam is cut off and differs in the last rak'ah: Does he complete his prayer like one who missed one or more rak'ahs, or does he repeat his prayer, or is his prayer valid?

If the Imam's voice cuts off and it is not possible to follow him, the worshipper (ma'mum) completes his prayer by himself, and is not required to repeat it. If it is not possible to know the Imam's transitions after the voice cuts off, then one should separate from the Imam. It is permissible to put forward someone to lead the rest of the prayer in place of the Imam whose voice cut off.