PHP Excel isDateTime not working - php

Question

I'd like some help to solve a problem with the PHP Excel library to import a cell data.
In my script I need to check if a cell is formatted as a date, using "PHPExcel_Shared_Date::isDateTime".
For some date cells, the format is flagged by MS Excel like this :
"Date formats that begin with an asterisk (*) respond to changes in regional date and time settings that are specified for the Operating System."
And for thoses cells, the test PHPExcel_Shared_Date::isDateTime fails, I obtain this :
$reader = PHPExcel_IOFactory::createReaderForFile($filepath);
$objexcel = $reader->load($filepath);
$cell = $objexcel->getSheet()->getCell('A2');
var_dump(PHPExcel_Shared_Date::isDateTime($cell)); // return false
echo $cell->getFormattedValue(); // return timestamp : 43466
When I convert my xlsx file in xls file or when I give another date format to my cell, it works, I obtain this :
$reader = PHPExcel_IOFactory::createReaderForFile($filepath);
$objexcel = $reader->load($filepath);
$cell = $objexcel->getSheet()->getCell('A2');
var_dump(PHPExcel_Shared_Date::isDateTime($cell)); // return true
echo $cell->getFormattedValue(); // return 2019-01-01
The "setReadDataOnly" is still at false for my reader.
Does someone has any idea to fix it ?
(I precise that i'm in France, and we write dates at format 'd/m/Y')
Thanks in advance for helping me.