Error when merging cells, how to fix?

Question

PHP

Hello!
PHP+PHPSPREADSHEET
Initially merge cells horizontally

$worksheet->mergeCells('F11:P11');
$worksheet->mergeCells('F12:P12');

Everything is merged normally, but after that I need to merge these cells vertically, I do this. The code works without errors, but when I open the file in Excel, the message "Error in the content part of the workbook 1.xlsx Do you want to try to restore?" I press yes. Correction window: Deleted entries: Merging cells from a part ..... Can someone come across a thread?
$worksheet->mergeCells('F11:F12');