Hi,
Unfortunately, I was unable to reproduce this issue on the default installation of X-Cart 4 on PHP Version 7.1.6.
Could you please provide me with the valid SSH/FTP or Control Panel access info to your server so I can see whats causing the issue directly.
Please post it in X-Business access list section here:
https://secure.x-cart.com/customer.php?target=create_access_info
Thank You.