Scripts de aplicativos - .getLastColumn() funciona uma vez em um loop for e depois gera erros

Estou tentando fazer um loop em Sheets e getLastColumn(). Eu ativo a primeira planilha e obtenho a última coluna, então ativo a próxima planilha, mas dessa vez recebo um erro em getLastColumn(). Estou fazendo isso em um loop for, pode ser esse o problema?

    //sort fab, milling, turning, engraving
    sheet = SpreadsheetApp.getActive().getSheetByName("Fab Schedule");
    sheet.activate;
  
    var lastColumnFab = sheet.getLastColumn();
    var lastColumn = lastColumnFab;
    var lastColumnMilling;
    var lastColumnTurning;
    var lastColumnEngraving;
    var currentSheet = SpreadsheetApp.getActiveSheet().getSheetName(); 
    Logger.log(currentSheet);

    for(a=0;a<3;a++){ // 'a' is for looping through the different sheets
    Logger.log(a);

    // counting non-empty rows 
    var BValues = sheet.getRange("B3:B").getValues();
    var i=0;
    var singleBValue = "";
    //Logger.log(BValues[i]);
    for(i = 0; BValues[i] != ""; i++){
      singleBValue = BValues[i];
      //console.log({i,singleBValue});
    }
    var lastRow = i;
    i=i+3;

    // arrays begin with 0 // all rows and columns begin with 1
    sheet.getRange(3,2,lastRow,lastColumn).activate();
    //sheet.getRange('B3:V').activate(); //number of columns is different on every
    sheet
    var statusColumn = getHeaderNumber("Status")+1; //get header uses array, so it
    starts at 0
    var dueDateColumn = getHeaderNumber("Due Date")+1;
    var engineerColumn = getHeaderNumber("Engineer")+1;
  
    //sort by incomplete->complete, then
    sheet.getActiveRange().sort([{column: statusColumn, ascending: false}, {column: dueDateColumn, ascending: true},{column:engineerColumn, ascending: true}]);
  //sheet.getActiveRange().sort([{column: 14, ascending: false}]);//, {column: 18, ascending: true},{column:2, ascending: true}]);

  sheet.getRange(3,14,lastRow,lastColumn-14).setHorizontalAlignment("center"); //number of columns is different on every sheet
  sheet.getRange(3,1,lastRow,lastColumn).setVerticalAlignment("middle");
  sheet.getRange(3,1,lastRow,lastColumn).setFontFamily("Arial");
  sheet.getRange(3,1,lastRow,lastColumn).setFontSize(10);
  if (a==0){
      sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Milling Schedule");
      sheet.activate();
      var currentSheet = SpreadsheetApp.getActiveSheet().getSheetName(); 
      Logger.log(currentSheet);
      lastColumnMilling = sheet.getLastColumn(); //error?
      lastColumn = lastColumnMilling;
    }

Exception: The coordinates of the range are outside the dimensions of the sheet. Sortbyincompleteanddate @ sort.gs:62