AH01071: Got error 'PHP message: PHP Warning: call_user_func_array() expects parameter 1 to be a valid callback, function 'csbs_replace_woocommerce_template_loop_product_link_open' not found or invalid function name i code example

Example: Warning: call_user_func_array() expects parameter 1 to be a valid callback

Somewhere in your theme or plugins is a line like this:

add_filter( 'something', 'regis_options' );
Could also be add_action(). Find that piece of code and remove or fix it.