Undefined Property Error

Since I’ve updated to WordPress 5.1.1, I’ve been getting the following error messages in the backend of my site:

Notice: Undefined property: stdClass::$map_meta_cap in /var/www/vhosts/[domain-name].com/httpdocs/wp-includes/post.php on line 1504

Notice: Undefined property: stdClass::$map_meta_cap in /var/www/vhosts/[domain-name].com/httpdocs/wp-includes/post.php on line 1525

I’ve updated to version 1.2.11.3 of Min and Max Quantity for WooCommerce. This error message only shows up when this plugin is active, and as soon as I deactivate the plugin, the error message goes away.

Do you know what may be going on and how I can fix this? Thanks.