Hi Jaikor,
Thanks for writing in! Please note that the latest X/Pro compatible WooCommerce version is 3.5.1
and it seems that you’re using v3.5.2 on your site. You can rollback to the earlier version by downloading it directly.
https://github.com/woocommerce/woocommerce/archive/3.5.1.zip
For future reference, kindly check our version information guide and changelog first, before updating anything.
With regard to those warnings, what you are seeing is the WooCommerce template notices. The template notices don’t actually cause any bugs or issues. The version of those template files just needs to be updated which our developers is already working on it. This notices will be removed when we roll out our next release update cycle anytime soon.
Also with regard to WooCheckout editor PHP errors, make sure that you’re running PHP v5.6.x or later to avoid incompatibility issues. Since you’re getting PHP notices, you can also ignore it by disabling your WP_DEBUG mode on your WordPress. Please refer to the following guide (https://codex.wordpress.org/WP_DEBUG).
Thank you for your understanding.