Fatal Error

Hello,
when editing a woocommerce product, creating a variable product and try to add a variant an ajax request to add the productvariant fails with an error 500.
In my debug.log I found the location:
PHP Fatal error: Uncaught TypeError: call_user_func_array(): Argument #1 ($function) must be a valid callback, class YWSBS_Product_Post_Type_Admin does not have a method “add_custom_fields_for_variation_products” in ../wp-includes/class-wp-hook.php:307
And yes this method does not exist in this class.
Removing this Line helps that the Productvariant loads but I do not have the option to check “Subscription” at the variant level of the product. Only if I create a normal product I’m able to check “Subscription”

Thank you