Google Sheets script: loop runs properly once, then throws an error

Following is a standalone Google Apps script I cobbled together (with very little programming experience). Basically, it's supposed to cycle through all the Google Sheets workbooks in a Google Drive folder. For each workbook, it hides all sheets except the one named "Current;" downloads that sheet as a PDF; then creates a new blank "Current" sheet. This worked perfectly 8 months ago. But now it works for the first workbook in the folder, then fails on the second workbook with the error, "Exception: You can't hide all the sheets in a document" on this line:

if(sheets[i].getName()!="Current"){ sheets[i].hideSheet() }

Here's the complete script:

function saveInvoice() {

  //This script will process all the mentor invoices as follows:
  // 1. Get all the workbooks in the invoice folder
  // 2. For each workbook:
  //    a. Turn the "Current" tab into a PDF and save it in the designated folder with filename "[mentor name]-[date].pdf"
  //    b. Rename "Current" to today's date
  //    c. Make a new "Current" from the blank invoice template
  //    d. Move the new Current to be the leftmost tab in the workbook
  //    e. Lather, rinse, repeat.


//get the speadsheets in the current folder
var invoiceFolder = DriveApp.getFoldersByName("Fake invoices for testing").next(); //THE FOLDER NAME NEEDS TO BE UPDATED EVERY YEAR! This is the folder with the speadsheet invoices.
var invoiceSheets = invoiceFolder.getFilesByType(MimeType.GOOGLE_SHEETS);
Logger.log(invoiceSheets)


while (invoiceSheets.hasNext()) // Loops through all Workbooks inside the folder.
  {
    var workBook = invoiceSheets.next(); //get the next workbook
    Logger.log("Workbook:"+workBook)


    var spreadSheet = SpreadsheetApp.open(workBook).getSheetByName("Current");
    Logger.log("spreadSheet:"+spreadSheet)


      // download the "Current" invoice sheet as a PDF named [mentor name (from cell A1)]+current date].pdf

        var today=new Date();
        var date = Utilities.formatDate(new Date(), "GMT+1", "yyyy-MM-dd") //get today's date and format it

      
        var sheets=SpreadsheetApp.open(workBook).getSheets(); //get all the sheets

        var ltrsht = SpreadsheetApp.open(workBook).getSheetByName("Current");


        //now cycle through the sheets in the workbook and hide all except "Current." Have to hide them b/c no way to d.l. a single sheet
        for(var i =0;i<sheets.length;i++){
          if(sheets[i].getName()!="Current"){ sheets[i].hideSheet() }
          }
          var pdf = DriveApp.getFileById(workBook.getId());
          var theBlob = pdf.getBlob().getAs('application/pdf').setName(ltrsht.getRange("A1").getValue()+"-"+date+".pdf"); //create the file name
          var folderID = "13KcgTUC3sw1aAa3xQWY6FkY6GwAH0cT7"; // Folder id to save in a folder **NEEDS TO BE UPDATED EVERY YEAR**
          var folder = DriveApp.getFolderById(folderID); //get the target folder
          var newFile = folder.createFile(theBlob); //save the file
      


      //now unhide the other sheets
       var sheets=SpreadsheetApp.open(workBook).getSheets(); //get all the sheets
        for(var i =0;i<sheets.length;i++){
          if(sheets[i].getName()!="Current"){ sheets[i].showSheet() }
          }


      //change name of "Current" sheet to today's date
      SpreadsheetApp.open(workBook).getSheetByName("Current").setName(date);


      //Make a copy of the "Blank" sheet and rename it "Current"
      var source = SpreadsheetApp.open(workBook);
      Logger.log("source:"+source)
      var sheet = SpreadsheetApp.open(workBook).getSheetByName('Blank');

      sheet.copyTo(SpreadsheetApp.open(workBook)).setName('Current');


      // Make the new Current sheet the leftmost tab in the Workbook
      // var tab = SpreadsheetApp.open(workBook).getSheetByName('Current');
      // SpreadsheetApp.open(workBook).setActiveSheet(tab);
      // SpreadsheetApp.open(workBook).moveActiveSheet(1);

      const dss = SpreadsheetApp.open(workBook);
      const sh = dss.getSheetByName('Current').activate();
      dss.moveActiveSheet(0);
  }

}

I suspect I'm missing something obvious because of my inexperience. What's especially puzzling is the fact that this same script worked flawlessly a year ago. Any guidance is much appreciated!

The error is a result of the "Current" sheet either being hidden or not existing in the given Spreadsheet. Modified it to log anytime a spreadsheet doesn't have a "Current" sheet and to show the "Current" sheet before hiding the rest. I also made some improvements that should speed things up with fewer calls to SpreadsheetApp.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

function saveInvoice() {
//This script will process all the mentor invoices as follows:
// 1. Get all the workbooks in the invoice folder
// 2. For each workbook:
//    a. Turn the "Current" tab into a PDF and save it in the designated folder with filename "[mentor name]-[date].pdf"
//    b. Rename "Current" to today's date
//    c. Make a new "Current" from the blank invoice template
//    d. Move the new Current to be the leftmost tab in the workbook
//    e. Lather, rinse, repeat.
//get the speadsheets in the current folder
var invoiceFolder = DriveApp.getFoldersByName("Fake invoices for testing").next(); //THE FOLDER NAME NEEDS TO BE UPDATED EVERY YEAR! This is the folder with the speadsheet invoices.
var invoiceSheets = invoiceFolder.getFilesByType(MimeType.GOOGLE_SHEETS);
Logger.log(invoiceSheets)
// Loops through all Workbooks inside the folder.
while (invoiceSheets.hasNext()) {
var workBook = invoiceSheets.next(); //get the next workbook
Logger.log("Workbook:" + workBook)
var spreadSheet = SpreadsheetApp.open(workBook);
var ltrsht = spreadSheet.getSheetByName("Current");
Logger.log("spreadSheet:" + ltrsht)
if (!ltrsht) {
Logger.log("Current invoice not found:" + spreadSheet);
} else {
// download the "Current" invoice sheet as a PDF named [mentor name (from cell A1)]+current date].pdf
var today = new Date();
var date = Utilities.formatDate(new Date(), "GMT+1", "yyyy-MM-dd") //get today's date and format it
var sheets = spreadSheet.getSheets(); //get all the sheets
//now cycle through the sheets in the workbook and hide all except "Current." Have to hide them b/c no way to d.l. a single sheet
ltrsht.showSheet();
for (var i = 0; i < sheets.length; i++) {
if (sheets[i].getName() != "Current") {
sheets[i].hideSheet()
}
}
var pdf = DriveApp.getFileById(workBook.getId());
var theBlob = pdf.getBlob().getAs('application/pdf').setName(ltrsht.getRange("A1").getValue() + "-" + date + ".pdf"); //create the file name
var folderID = "13KcgTUC3sw1aAa3xQWY6FkY6GwAH0cT7"; // Folder id to save in a folder **NEEDS TO BE UPDATED EVERY YEAR**
var folder = DriveApp.getFolderById(folderID); //get the target folder
var newFile = folder.createFile(theBlob); //save the file
//now unhide the other sheets
for (var i = 0; i < sheets.length; i++) {
if (sheets[i].getName() != "Current") {
sheets[i].showSheet();
}
}
//change name of "Current" sheet to today's date
ltrsht.setName(date);
//Make a copy of the "Blank" sheet and rename it "Current"
Logger.log("source:" + spreadSheet)
var blank = spreadSheet.getSheetByName('Blank');
var sh = blank.copyTo(spreadSheet).setName('Current');
// Make the new Current sheet the leftmost tab in the Workbook
// var tab = SpreadsheetApp.open(workBook).getSheetByName('Current');
// SpreadsheetApp.open(workBook).setActiveSheet(tab);
// SpreadsheetApp.open(workBook).moveActiveSheet(1);
sh.activate();
spreadSheet.moveActiveSheet(0);
}
}
}

<!-- end snippet -->