The = in "=_DateRDV:" is the problem here. The package reads this as a Formula. The Formula does not exist and gives an error.
Depending on if you want to export a string for this cell or format the whole column to text, you can take a different approach here. You can make use of export formatting goodies when exporting with Maatbesite Laravel Exel.
Either one of these approaches will help you out hopefully:
- Custom formatting values and set the Datatype to DataType::TYPE_STRING
- Formatting Columns for formatting the whole column to any of these options