Unable to upload *.vcf files. WP Core Versions 4.9.9 – 5.0.3

Uploading VCF files gets me the error “Sorry, this file type is not permitted for security reasons.”

Not working on Core Versions 4.9.9/5.0.3
It is working on Core Version 4.9.5

The filter function to add the mime types doesn’t help.

add_filter('upload_mimes', function( $existing_mimes = array() ) {
  $existing_mimes['vcf'] = 'text/x-vcard';
  return $existing_mimes;
});

The define('ALLOW_UNFILTERED_UPLOADS', true); in wpconfig helps but this is not a solution.

Thoughts?