Inserting blank rows now running very slow

This block of code inserts a blank row at every change in column A. The loop begins at the bottom. This used to run extremely fast. Now it's slow. Any ideas why?

   Dim firstRow As Integer
    Dim currentRow As Integer
    
    firstRow = 2
  
    
    For currentRow = Range("A1048576").End(xlUp).Row To firstRow Step -1
        If Range("A" & currentRow) <> Range("A" & currentRow).Offset(-1, 0) Then
           Range("A" & currentRow).EntireRow.Insert
        End If
    
    Next

There is other code in this procedure. For some reason it takes a long time. When I run this code in its own procedure it zips right thru.