There was an error:
Strict Standards: call_user_func_array() expects parameter 1 to be a valid callback, non-static method WooCommerce_Product_Finder_Admin::init() should not be called statically
I’ve fixed it but widgets aren’t shown. So, I’ve deactivated other plugins and activated default WordPress theme. The problem was present there too. So the issue isn’t caused by our theme, but the plugin WooCommerce Product Finder. You can check it yourself. Change the theme to the default WordPress one and you’ll see the problem with widgets persists there as well.
So you have to contact Woocommerce support team to investigate the issue. Tell them to check the plugin with default theme.