Hey! I've been having this issue among others recently, I have found/developed a workaround for this. You can use this function to delete rows from a worksheet:

function deleteRows(worksheet, start, count, rowCount) {
	for (let i = 0; i < count; i++) {
		if (rowCount && start + i === rowCount) {
			// Workaround fix for deleting the last row.
			worksheet.spliceRows(start, 1, []);
		}
		else {
			worksheet.spliceRows(start, 1);
		}
	}
}

With this, rowCount is optional, pass it in if you may be deleting the last row - it will detect when the last row is being deleted; the workaround is to insert a blank row in place of the last row (which works!). I found that deleting multiple rows at once doesn't usually work, so my function deletes them one at a time.

Hope this helps.

Still exists at exceljs@4.3.0

I have the same problem. exceljs@4.3.0

This code has allowed me to work around the problem.
Note, however, that worksheet.rowCount will not be reduced because a blank row is inserted at the end.

test('rowCount will not be reduced', () => {
  const wb = new ExcelJS.workbook();
  const ws = wb.addWorksheet();
  ws.addRows([['1st'], ['2nd'], ['3rd']);
  
  deleteRows(ws, 2, 2, ws.rowCount);
  
  expect(ws.rowCount).not.toBe(1);
});

function deleteRows(worksheet, start, count, rowCount) {
	for (let i = 0; i < count; i++) {
		if (rowCount && start + i === rowCount) {
			// Workaround fix for deleting the last row.
			worksheet.spliceRows(start, 1, []);
		}
		else {
			worksheet.spliceRows(start, 1);
		}
	}
}