What is the authenticity, in terms of chain of narration (sanad) and text (matn), of the story of our master Umar and the son of our master Amr ibn al-Aas (may Allah be pleased with them both)? And does its mention in a previous fatwa on your website contradict its historical invalidity?

The story mentioned was narrated by Ibn Abd al-Hakam in "Futuh Misr wal-Maghrib" with an incomplete chain of transmission (sanad), as he said, "Haddathana (he narrated to us)," and one of its narrators, Abu Abdah — Yusuf ibn Abdah — was deemed weak by some scholars because he narrated objectionable (munkar) hadiths from Thabit and Humayd, and he narrates this story from both of them.