VBA Delete entire row if value is less than specified value - deletes wrong rows

I'm attempting to run a small macro that searches column S of a worksheet and if the value in column S is <0.501, it deletes that row.

The code I am running at the moment deletes some rows but appears to do so randomly rather than based on the cell value in s. Can anyone see where my error is coming from?

Sub sort_delete_500cust()

         Dim WS_Count As Integer
         Dim I, K As Integer
         Dim endrow As Long

         ' Set WS_Count equal to the number of worksheets in the active
         ' workbook.
         WS_Count = Workbooks("Standard.xlsx").Worksheets.count

         ' Begin the loop.
         For I = 1 To WS_Count

            With Worksheets(I)

                endrow = .Range("a" & .Rows.count).End(xlUp).row ' only works if cells are unmerged
                Range("A2:v2" & endrow).Sort _
                Key1:=Range("s2"), Order1:=xlDescending 'key is the sort by column

                                For K = 2 To endrow

                        If .Cells(K, 19).Value < 0.501 Then
                        .Range("S" & K).EntireRow.Delete

                        End If

                    Next K

            End With

         Next I

      End Sub

Cheers!