Ensures custom SSH2 class is loaded before autoloader is triggered by class_exists

preload-ssh2.php

<?php
/*
Plugin Name: Preload SSH class
Plugin URI: https://wordpress.org/support/topic/conflict-with-ssh-sftp-updater-support-ssh2-fs_method/
Description: Ensures custom SSH2 class is loaded before autoloader is triggered by class_exists
Author: Tim Whitlock
*/

function filter_filesystem_method( $method = '' ){
    if( 'ssh2' === $method && ! class_exists('WP_Filesystem_SSH2',false) ){
        if( $path = phpseclib_filesystem_method_file('','ssh2') ){
            require_once $path;
        }
    }
    return $method;
};

add_filter('filesystem_method','filter_filesystem_method',10,1);