أَنْ لَا يُقْصَدَ تَشْرِيكُ الْجُمْلَتَيْنِ فِي الْحُكْمِ لِقِيَامِ مَانِعٍ
The two clauses must not share the same grammatical scope because an impediment prevents that reading.
In the fifth case, the clauses are neither complete restatements nor unrelated. They have a meaningful connection, but coordination would bring the second under an earlier quotation, condition, or other governing expression.
Thus the case is intermediate between complete connection and disconnection. Omission of wāw prevents an unintended shared grammatical status, not a connection in meaning.