Problem
At various times, for example when saving settings, the following message may appear:
.../wp-admin/includes/class-wp-filesystem-ftpext.php:438: ftp_nlist: Argument #1 (Sftp) must be of type FTP\Connection, null givenCause
The server is misconfigured, preventing the PHP process from creating files. As a result, WordPress attempts to create the file required by Borlabs Cookie via FTP instead.
For more information about the WordPress Filesystem API, please refer to: https://codex.wordpress.org/Filesystem_API
Solution
Solution A
Please contact your server administrator and ask them to adjust the file permissions so that the PHP process can create files.
Solution B
Add the required FTP credentials to your WordPress configuration file (wp-config.php).
For more information, please refer to: https://developer.wordpress.org/apis/wp-config-php/