What's the issue?

Currently, numerical values cannot be stored in columns. The reason is that numbers incorrectly end up in "shared strings" and their indexes are ending up in the cell - not the values itself.

Want a quick fix?

change this

into that

$cells[] = sprintf(
	'<c r="%s" t="%s"><v>%s</v></c>',
	$this->escape_xml( $this->xlsx_cell_name( $row_no, $col_no ) ),
	$this->escape_xml( $field_type ),
	$this->escape_xml( $field_type === 'n' ? $field_value : $field_value_no )
);

Make it even better

Put the creation of $field_value_no into an else clause.

To reproduce the issue, try to generate two xlsx files, like :

$zipper1 = new \ZipArchive;
$file1 = DIR . '/file1.xlsx';
$zipper1->open( $file1, \ZipArchive::CREATE | \ZipArchive::OVERWRITE );
$builder1 = new XlsxBuilder( $zipper1 );
$builder1->add_rows( $FirstDataArray );
$builder1->build();
$zipper1->close();

(tried here to unset $builder and $zipper, but with no success)

$zipper2 = new \ZipArchive;
$file2 = DIR . '/file2.xlsx';
$zipper2->open( $file2, \ZipArchive::CREATE | \ZipArchive::OVERWRITE );
$builder2 = new XlsxBuilder( $zipper2 );
$builder2->add_rows( $SecondDataArray );
$builder2->build();
$zipper2->close();

Both files are generated. First file is ok.. second, it's garbled.
With the same code, If the first block is commented, second file become perfect.

I cannot find the leak....