Code skips on Run Mode but runs fine on F8 (Debug Mode)

Hi! I have a code that finds the duplicates of column A and merges some columns on the same row according to how many duplicates are in the column A.

When I run the code pressing F8 everything works marvelous but when I run it as it's supposed to run (F5) then it just won't merge anything.

Can anyone help me, please? This is driving me nuts and it's the last thing I need to fix for presenting a project to my boss

Application.DisplayAlerts = False
    With Application.WorksheetFunction
    Dim count As Integer
        For i = 4 To 40
            If Sheet3.Range("A" & i) = Sheet3.Range("A" & i).Offset(1, 0) And Sheet3.Range("A" & i) <> "" Then
                count = .CountIf(Sheet3.Range("A4:A44"), Sheet3.Range("A" & i))
                Sheet3.Range("A" & i & ":" & "A" & i + count - 1).Select
                Selection.Merge
                Sheet3.Range("N" & i & ":" & "N" & i + count - 1).Select
                Selection.Merge
                Sheet3.Range("B" & i & ":" & "B" & i + count - 1).Select
                Selection.Merge
                Sheet3.Range("C" & i & ":" & "C" & i + count - 1).Select
                Selection.Merge
                Sheet3.Range("D" & i & ":" & "D" & i + count - 1).Select
                Selection.Merge
                Sheet3.Range("E" & i & ":" & "E" & i + count - 1).Select
                Selection.Merge
                Sheet3.Range("F" & i & ":" & "F" & i + count - 1).Select
                Selection.Merge
                Sheet3.Range("G" & i & ":" & "G" & i + count - 1).Select
                Selection.Merge
                Sheet3.Range("H" & i & ":" & "H" & i + count - 1).Select
                Selection.Merge
                Sheet3.Range("I" & i & ":" & "I" & i + count - 1).Select
                Selection.Merge
                Sheet3.Range("J" & i & ":" & "J" & i + count - 1).Select
                Selection.Merge
                Sheet3.Range("M" & i & ":" & "M" & i + count - 1).Select
                Selection.Merge
                i = i + count - 1
            End If
        Next
    End With

Thanks for reading ^^