if you have Advance Custom field Pro,
might it crashed with WC 3.
to solve this, please follow temporary instruction below :
1. open select.php at (wp-content/plugins/acf-pro/fields/select.php
2. find function input_admin_enqueue_scripts()
3. change $script = acf_get_dir(“assets/inc/select2/3/select2{$min}.js”); to be $script = acf_get_dir(“assets/inc/select2/4/select2{$min}.js”);
4. change $style = acf_get_dir(“assets/inc/select2/3/select2.css”); to be $style = acf_get_dir(“assets/inc/select2/4/select2.css”);
with this “temporary” solution, hope this can help other wc devs.