PHPspreadsheet only saves "Sheet1" when xlsx but is ok when xls

Question

I'm using PHPSpreadsheet to generate an XLSX file. the code

$spreadsheet->setActiveSheetIndex(0);
$writer = new Xlsx($spreadsheet);
$full_filename = $path . $filename . '.xlsx';
$writer->save($full_filename);

When using the above code file only contains "Sheet1" and is blank but when I use

$spreadsheet->setActiveSheetIndex(0);
$writer = new Xls($spreadsheet);
$full_filename = $path . $filename . '.xls';
$writer->save($full_filename);

above code save the correct data with multiple sheets.

Saving XLSX used to work last week.

My server is:

• Ubuntu 18.04 LTS
• Mariadb 10
• PHP 7.2.10 using Yii2 framework
• using phpoffice/phpspreadsheet v. 1.3.1