Issue with splitting Excel file (.xlxs) with Powershell based on column values - powershell

Question

I have the below script that was posted here: Split Excelfile .xlxs with Powershell based on column values and it works as described but I am experiencing an issue.
The script will check one xlsx file and sort the content by unique values in column A and then copy these data set and create a new file.
The issue I am having is out of about 4000 files, 20 of them are created with the full data set from the original file. The rest of the files a split and created correctly. Not sure as to why this is occurring. Any help is appreciated.
Function Create-Excel-Spreadsheet {
Param($NameOfSpreadsheet)
# open excel
$excel = New-Object -ComObject excel.application
$excel.visible = $true
# add a worksheet
$workbook = $excel.Workbooks.Add()
$xl_wksht= $workbook.Worksheets.Item(1)
$xl_wksht.Name = $NameOfSpreadsheet
return $workbook
}
$objexcel = New-Object -ComObject Excel.Application
$wb = $objexcel.WorkBooks.Open("C:\Temp\Test.xlsx") # Changing path for test.xlsx file.
$objexcel.Visible = $true
$objexcel.DisplayAlerts = $False
$ws = $wb.Worksheets.Item(1)
$usedRange = $ws.UsedRange
$usedRange.AutoFilter()
$totalRows = $usedRange.Rows.Count
$rangeForUnique = $usedRange.Offset(1, 0).Resize($UsedRange.Rows.Count-1)
[string[]]$UniqueListOfRowValues = $rangeForUnique.Columns.Item(1).Value2 | sort -Unique
for ($i = 0; $i -lt $UniqueListOfRowValues.Count; $i++) {
$newRange = $usedRange.AutoFilter(1, $UniqueListOfRowValues[$i])
$workbook = Create-Excel-Spreadsheet $UniqueListOfRowValues[$i]
$wksheet = $workbook.Worksheets.Item(1)
$range = $ws.UsedRange.Cells
$range.Copy()
$wksheet.Paste($wksheet.Range("A1"))
$workbook.SaveAs("C:\temp\" + $UniqueListOfRowValues[$i], $xlFixedFormat)
$workbook.Close()
}