Why is الْكَافِرِينَ mansub in لَكِنَّ الْكَافِرِينَ جَاهِلُونَ?

Introduction to Mansubat and the Ism of Inna

• It is a mudaf ilayh.
• It is the fa'il.
• It is the ism of لَكِنَّ, with ya as its sign of nasb.
• It is the khabar of لَكِنَّ.