Ok, I have worked it all out now, everything works perfect, adding and removing.
Filename = class.yith-wcwl-init.php
Change;
var yith_wcwl_plugin_ajax_web_url = '<?php echo admin_url('admin-ajax.php') ?>';
TO
var yith_wcwl_plugin_ajax_web_url = '<?php echo admin_url('admin-ajax.php', (is_ssl() ? 'https' : 'http')) ?>';
Filename = class.yith-wcwl-init.php
Change;
var login_redirect_url = '<?php echo wp_login_url() . '?redirect_to=' . urlencode( $_SERVER['REQUEST_URI']) ?>';
TO
var login_redirect_url = '<?php echo wp_login_url() . '?redirect_to=', (is_ssl() ? 'https' : 'http') . urlencode( $_SERVER['REQUEST_URI']) ?>';
Filename = class.yith-wcwl-init.php
Change;
'<a href="' . admin_url( 'admin.php?page=' . $wc_settings_page . '&tab=yith_wcwl' ) . '">' . __( 'Settings', 'yit' ) . '</a>',
TO
'<a href="'http') . $wc_settings_page . '&tab=yith_wcwl' ) . '">' . __( 'Settings', 'yit' ) . '</a>',
Filename = class.yith-wcwl-ui.php
Change;
$html .= '<img src="' . esc_url( admin_url( 'images/wpspin_light.gif' ) ) . '" class="ajax-loading" id="add-items-ajax-loading" alt="" width="16" height="16" style="visibility:hidden" />';
TO
$html .= '<img src="' . esc_url( admin_url( 'images/wpspin_light.gif', (is_ssl() ? 'https' : 'http') ) ) . '" class="ajax-loading" id="add-items-ajax-loading" alt="" width="16" height="16" style="visibility:hidden" />';
Filename = class.yith-wcwl.php
Change;
return admin_url( 'admin-ajax.php?wishlist_item_id=' . $item_id);
TO
return admin_url( 'admin-ajax.php?wishlist_item_id=' . $item_id, (is_ssl() ? 'https' : 'http'));
The plugin now works PERFECTLY for me now, I am no longer having issues with it working, on FORCE ADMIN SSL or otherwise.
For someone who knows nothing about PHP, I have done what the makers of the plugin could not do it seems.
I have tested this on two different themes that were not working previously – both now work.
If you have a cache plugin such as WP Super Cache, make sure you clear the cache (I removed mine totally from wp-config and disabled the plugin).
It is scary that the people who made this plugin also make e-commerce themes and are not using SSL or even testing their plugins with SSL active.