Why Does this Macro Keep Deleting ALL of the Data - excel

Question

I have this Macro that copies one sheet from another Workbook that i open via a File Dialog. It is supposed to sort and delete the Rows whose A Column does not possess data in an Array I've defined. It appears to be copying and pasting the data properly but when it runs through the loop to delete the data that doesn't contain the items in the array it ends up clearing the entire sheet
This Macro worked last Friday when I left for the day but now it seems it no longer works. I've tried stepping through the code but the loop doesn't appear to change much so I'm unsure why it stopped working over the weekend.
Public filepath As String
Sub SPOMacro()
'Display a Dialog Box that allows to select a single file.
'The path for the file picked will be stored in fullpath variable
With Application.FileDialog(msoFileDialogFilePicker)
'Makes sure the user can select only one file
.AllowMultiSelect = False
'Filter to just the following types of files to narrow down selection options
.Filters.Add "Excel Files", "*.xlsx; *.xlsm; *.xls; *.xlsb", 1
'Show the dialog box
.Show
'Store in fullpath variable
fullPath = .SelectedItems.Item(1)
End With
filepath = fullPath
'It's a good idea to still check if the file type selected is accurate.
'Quit the procedure if the user didn't select the type of file we need.
If InStr(fullPath, ".xls") = 0 Then
Exit Sub
End If
'Open the file selected by the user
'Workbooks.Open fullpath
'This is the Copy Sheet Portion
'MsgBox filepath
Dim spo_book As Workbook
Dim target_book As Workbook
Set spo_book = Workbooks("SPO_Untimed_Report.xlsm")
Set target_book = Workbooks.Open(filepath)
Dim dst_sheet As Worksheet
Dim target_sheet As Worksheet
Set dst_sheet = spo_book.Sheets("SPO Data")
Set target_sheet = target_book.Sheets("Untimed Parts")
dst_sheet.Cells.Clear
dst_sheet.Cells.Delete
Z = Cells(Sheets("Untimed Parts").Rows.Count, 1).End(xlUp).Row
target_sheet.Range("A1:R" & Z).Copy
dst_sheet.Range("A1").PasteSpecial
' Sort Pasted Data by Cost Ctr
Dim dontDelete
dontDelete = Array("RX01225", "RX01303", "RX01304", "RX01314", "RX01338", "Cost Ctr")
dst_sheet.Activate
Dim i As Long, j As Long
Dim isThere As Boolean
For i = Range("A" & Rows.Count).End(xlUp).Row To 1 Step -1
For j = LBound(dontDelete) To UBound(dontDelete)
If StrComp(Range("A" & i), dontDelete(j), vbTextCompare) = 0 Then
isThere = True
End If
Next j
If Not isThere Then
Range("A" & i).Delete shift:=xlUp
End If
isThere = False
Next i
'Deletes Blank Rows
Columns("A").SpecialCells(xlCellTypeBlanks).EntireRow.Delete
End Sub
The expected outcome is that the workbook that I called SPO Untimed will keep the sheet called SPO Data and the data that is pasted into that sheet from the Selected Workbook (By the File Dialog) is sorted by the Array I've defined and only the rows that have those items in the A Column remain.