An adjective ending in additional alif-nun is ghayr munsarif here when its feminine is not on فَعْلَانَةٌ.
سَكْرَانُ → سَكْرَىٰ
Because the feminine is سَكْرَىٰ, not سَكْرَانَةٌ, the taught condition is fulfilled.
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Situation 2: A Particular Adjective Form
Cause of Ghayr Munsarif: Additional Alif and Nun
An adjective ending in additional alif-nun is ghayr munsarif here when its feminine is not on فَعْلَانَةٌ.
سَكْرَانُ → سَكْرَىٰ
Because the feminine is سَكْرَىٰ, not سَكْرَانَةٌ, the taught condition is fulfilled.