Incompatibility with Simple Custom Post Order plugin

Found an incompatibility with the plugin “Simple Custom Post Order” by ColorLib. When trying to reorder WP pages around with that plugin, the log starts quickly filling with many of the following:

A non-numeric value encountered in \strong-testimonials\includes\class-strong-testimonials-order.php on line 280

After some cursory debugging around that line, it becomes apparent $query_vars['posts_per_page'] is not getting set, most probably because the function update_menu_order it resides, is being called from add_action( 'wp_ajax_update-menu-order', array( __CLASS__, 'update_menu_order' ) ); but it isn’t filtering the extraneous hook from the “Simple Custom Post Order” plugin. Think would need to make sure the aforementioned function is called only in ST context.

Thanks.