Custom So Widget only partially working (2 issues)

I followed the Create Widget page (would be nice if this had a complete source to go with it) – and have a widget that sort of works.
Two environments
1. Local – basic WP with TwentySeventeen theme + Plugins (these are the only active plugins)
Page Builder by SiteOrigin
SiteOrigin Widgets Bundle
My Custom Widget Plugin
2. Sever – Weaver Xtreme Theme – all the above plugins plus several more.
Local Issue
Local server: Widget shows in the Page builder. I can add it to a layout and it works perfectly – I can fill in the various data items – save and the values are retained.
However, when the page is opened nothing is displayed. I have put debug statements in the code for the get_template_name() and get_template_dir() – both of which get output. In the dump I output both the name / dir and do a print_r of the $instance – in both cases correct name and dir output and the Instance shows all the data captured in the widget.

The template does not render and debug statements placed in the template file do not show in the log.
In the generated page it appears the container for the widget is being created

<div class="so-widget-my-custom-widget so-widget-my-custom-widget-default-d75171398898"></div>

Live Server
Plugin does not install – even if I copy folder manually – does not show up in plugins page. If I do an upload – white screen of death – refresh shows the Plugin is installed – but there is no folder in plugins for it and (obviously) it does not show in widgets.

Plugin implementation
I have put the widget definition directly into the Plugin file (rather than registering a widget folder – earlier attempts with this did not work and with no sample to follow I decided to fall back to a simpler implementation).

/**
 * Plugin Name:   My Custom Widget
 * Plugin URI:    ***************
 * Description:   My Custom Widget
 * Version:       1.0
 * Author:        Julian Hansen
 * Author URI:    ***************
 */
class My_Custom_Widget extends SiteOrigin_Widget {
    function __construct() {
        parent::__construct(
           // as per create widget page and form fields page    
        )
    }
    function get_template_name($instance) {
        // Debug here - file_put_contents('trace.log', ....);    
        return 'default';
    }
    function get_template_dir($instance) {
        // Debug here - file_put_contents('trace.log', ....);    
        return plugin_dir_path(__FILE__) . 'tpl';
    }
}    
siteorigin_widget_register('lsow-clients', __FILE__, 'My_Custom_Widget');

my-custom-widget
  my-custom-widget.php
  tpl
     default.php

<?php
  // Debug here - file_put_contents('trace.log', ....);    
?>
<div>My Custom widget</div>