Ohne deine Datei ist das schwierig, wegen Testen.  Also ohne Garantie.  Der Fehler könnte gewesen sein, das Cells und Range ohne vorangestellte Sheetbezeichnung immer auf das aktive Sheet zeigt. Somit auf das Neuerstellte mit den Filterergebnissen.

Sub Reasoncode30()

    Dim fd     As Office.FileDialog
    Dim last_Row As Long
    Dim last_Column As Long
    Dim i      As Long
    Dim j      As Long

    Set fd = Application.FileDialog(msoFileDialogFilePicker)
    
    With fd
        .Filters.Clear
        .Title = "Bitte Mandant: " & Mandant & " auswählen"
        .Filters.Add "Excel Files", "*.xlsx?", 1
        .AllowMultiSelect = False
        Dim sFile As String
        
        If .Show Then sFile = .SelectedItems(1)
           
    End With
    Application.ScreenUpdating = False
    
    If sFile = "" Then Exit Sub
    Set ext_produkt = Workbooks.Open(sFile)
    
    'Ganze Spalte
    With Worksheets("F01")
        last_Row = .Cells(.Rows.Count, 3).End(xlUp).Row
        .Cells(1, .Range("H1").Column).AutoFilter .Range("H1").Column, "TB", Operator:=xlAnd, VisibleDropDown:=True
        .Cells(1, .Range("BO1").Column).AutoFilter .Range("BO1").Column, 30, Operator:=xlAnd, VisibleDropDown:=True
    End With
    
    Worksheets.Add
    ActiveSheet.Name = "SB und TB Auftrag"
    Worksheets("F01").Range("A1:BY" & last_Row).Copy Destination:=ActiveSheet.Range("A1")
    
    Dim wks    As Worksheet
    For Each ws In Worksheets
        If ws.AutoFilterMode Then
            ws.AutoFilterMode = False
        End If
    Next ws
        
    With Worksheets("F01")
        .Activate
        If Not .AutoFilterMode = True Then
            .Cells(m, .Range("H1").Column).AutoFilter .Range("H1").Column, "WB", Operator:=xlAnd, VisibleDropDown:=True
            .Cells(m, .Range("BO1").Column).AutoFilter .Range("BO1").Column, 30, Operator:=xlAnd, VisibleDropDown:=True
            
            Worksheets.Add
            ActiveSheet.Name = "WB Auftrag"
            .Range("A1:BY" & last_Row).Copy Destination:=ActiveSheet.Range("A1")
        End If
    End With
    Application.ScreenUpdating = True
End Sub