AfterUpdate() Recordset edit leads to "No current Record 3021"

Question

I'm using a form to enter a component ID (CID).
After entering the Number in the Field I use the AfterUpdate() function with CID to look up a corresponding Prod ID in another Table.
The Matching Prod ID from the other Table will then be entered automatically into the field. The field is a multivalued Field.

Private Sub Form_AfterUpdate()

Dim rst As DAO.Recordset
Dim rstChld As DAO.Recordset2

Dim tmpVar

If Me.Dirty Then
    Me.Dirty = False
End If

If StrComp(Me.Part, "Device") = 0 Then
    tmpVar = DLookup("[Device Prod]", "subLookTblCIDDevice", "[CID Device] = '" & Me.CIDDevice & "'")
    
    Set rst = Me.Recordset
    
    If Me.Recordset.RecordCount = 0 Then
        rst.MoveFirst
    End If
  
    If Not (rst.BOF And rst.EOF) Then
        If rst.Updatable Then
            rst.Edit
            Set rstChld = rst!Prod.Value
            rstChld.AddNew
            rstChld.Fields(0) = tmpVar
            rstChld.Update 
            rst.Update 
            
            Me.Bookmark = rst.LastModified
            
            Set rst = Nothing
            Set rstChld = Nothing
        End If
    End If
End If
End Sub    

If the record exists and I'm changing the CID the corresponding field gets its correct corresponding ID.

If it is a new Record and the first of the recordset I get the error message

No Current Record - 3021

It can be mitigated by adding

If Me.Recordset.RecordCount = 0 Then
    rst.MoveFirst
End If

But if it is a new Record and not the first record it changes the previous record.

I tried .AddNew instead of .Edit. This will create a new record after the one which has been updated.

I don't understand why it is jumping before or after the record.