CSV importer not working anymore: CSV not permitted

Hello!

My CSV importer does not work anymore. It used to work just fine in 4.6.2.
Error: “Sorry, this file type is not permitted for security reasons.”

The CSV file should be allowed as I can see in the wp-includes/functions.php:
‘csv’ => ‘text/csv’,

Anybody knows what to do?
Allowing all file types by changing wp-config.php is not an option.

Many thanks!