Woocommerce Checkout Details Doesn't Show Up

THE CORRECT WAY.... After filling out checkout form, customers will be automatically and instantly redirected to checkout details page with payment infos. BUT... what frustrated me is that instead of going automatically to payment infos, it keeps returning back to previous checkout form. SO... they won't see any kind of payment info afterwards. They can pay manually through "my-account" and click "orders" but this is not the case and is not that way. The payment page should go automatically after filling out form. One thing for sure it's NOT CAUSED by PLUGIN. I have tried many times deactivated all plugins and keep woocommerce remaining. Still did not work! My current hypothesis: - server migration (i was moved from different hosting) - due to nginx (I was previously using Apache then migrated to nginx a day before it happened) - change in MySQL version (not sure whether it's the issue or not) - using cloudlfare after migration (but has deactivated it) - something wrong within the css code or checkout endpoints