Hi @studio34
I don’t believe this underscore is an issue at all. There is no code in ACF which is exploding the $post_id string by the ‘_’ cahracter. Instead it looks in the wp_options table for a value with a options_name of:
'product_cat_' . $cat_id . '_' . $field_name
Perhaps you are having another issue but have jumped to this conclusion?
Let me know if I can be of any other help.
Perhaps you could test on another taxonomy just to rule this out?
