Après avoir adapté votre code à mon fichier, il bug dans la partie en gras ci-dessous.
Je ne sais pas si vous arrivez à comprendre sans le fichier.
Application.EnableEvents = False
    If Target.Address = "$D$4" Then
        If Target <> "" Then
            [D6] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 1)
            [D8] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 2)
            [D10] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 3)
            [D12] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 5)
            [D14] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 6)
            [D16] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 7)
            [D18] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 8)
            [D20] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 9)
            [D22] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 12)
            [D24] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 15)
            [D26] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 16)
            [D28] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 20)
            [D30] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 23)
            [G20] = Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 10)
        End If
    End If
    If Target.Address = "$D$6" Or Target.Address = "$D$8" Or Target.Address = "$D$10" Or Target.Address = "$D$12" Or Target.Address = "$D$14" Or Target.Address = "$D$16" Or Target.Address = "$D$18" Or Target.Address = "$D$20" Or Target.Address = "$D$22" Or Target.Address = "$D24" Or Target.Address = "$D$26" Or Target.Address = "$D$28" Or Target.Address = "$D$30" Or Target.Address = "$G$20" Then
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 1) = [D6]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 2) = [D8]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 3) = [D10]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 5) = [D12]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 6) = [D14]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 7) = [D16]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 8) = [D18]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 9) = [D20]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 12) = [D22]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 15) = [D24]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 16) = [D26]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 20) = [D28]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 23) = [D30]
        Feuil12.Cells(Application.Match([D4], [Dossier], 0) + 4, 10) = [G20]
    End If
    Application.EnableEvents = True