WooCommerce onSale Page Layered Nav widget fatal error

Hi,
On the sale product page, it seems that the WooCommerce onSale Page Layered Nav widgets is not working :
Firstly, I have problems to show it on the page (note that I use Widget options plugin and I need to check “hide on checked pages” to see it. If I choose “show on checked pages and choose Sale page it doesn’t appear.
When it appears, it produces a fatal error :
Here is the stack trace
Fatal error: Uncaught TypeError: Cannot access offset of type string on string in .../wp-content/plugins/on-sale-page-for-woocommerce/public/class-wc-onsale-page-widget-layered-nav.php:353 Stack trace: #0 .../wp-content/plugins/on-sale-page-for-woocommerce/public/class-wc-onsale-page-widget-layered-nav.php(405): WC_Onsale_Page_Widget_Layered_Nav->get_filtered_term_product_counts() #1 /wp-content/plugins/on-sale-page-for-woocommerce/public/class-wc-onsale-page-widget-layered-nav.php(167): WC_Onsale_Page_Widget_Layered_Nav->layered_nav_list() #2 /wp-includes/class-wp-widget.php(393): WC_Onsale_Page_Widget_Layered_Nav->widget() #3 /wp-includes/widgets.php(835): WP_Widget->display_callback() #4 /wp-content/themes/oceanwp/sidebar.php(24): dynamic_sidebar() #5 /wp-includes/template.php(770): require_once('...') #6 /wp-includes/template.php(716): load_template() #7 /wp-includes/general-template.php(136): locate_template() #8 /wp-content/themes/oceanwp/inc/helpers.php(689): get_sidebar() #9 /wp-includes/class-wp-hook.php(307): oceanwp_display_sidebar() #10 /wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters() #11 /wp-includes/plugin.php(476): WP_Hook->do_action() #12 /wp-content/themes/oceanwp/woocommerce/wc-content-wrapper-end.php(22): do_action() #13 /wp-includes/template.php(772): require('...') #14 /wp-includes/template.php(716): load_template() #15 /wp-includes/general-template.php(204): locate_template() #16 /wp-content/themes/oceanwp/inc/woocommerce/woocommerce-config.php(324): get_template_part() #17 /wp-includes/class-wp-hook.php(307): OceanWP_WooCommerce_Config::content_wrapper_end() #18 /wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters() #19 /wp-includes/plugin.php(476): WP_Hook->do_action() #20 /wp-content/plugins/woocommerce/templates/archive-product.php(96): do_action() #21 /wp-includes/template-loader.php(106): include('...') #22 /wp-blog-header.php(19): require_once('...') #23 /index.php(17): require('...') #24 {main} thrown in /wp-content/plugins/on-sale-page-for-woocommerce/public/class-wc-onsale-page-widget-layered-nav.php on line 353

Thank you