Hi there,
Thank you for reaching out!
I understand that after saving the standard tax rates in WooCommerce >> Settings >> Tax >> Standard rates, the row you’ve added simply disappears.
That does sound odd and the thread you’ve linked to seems to be slightly different – the tax rates were not applied on the cart/checkout pages. That seems to have been related to automated tax calculation with WooCommerce Services.
Can you please specify whether you are unable to save the tax rates in WooCommerce >> Settings >> Tax >> Standard rates or you are able to save the tax rates there but those aren’t applied during checkout? Also, are you using automated tax calculation with WooCommerce Services?
If the tax rates in WooCommerce >> Settings >> Tax >> Standard rates are not saved at all and automated tax calculation is not enabled in WooCommerce >> Settings >> Tax – there’s a chance this behaviour is caused by a plugin/theme conflict on your site as this is not something I am able to replicate on my own test site.
Read more about plugin and theme conflicts in the Self-Service Guide on WooCommerce.com.
How to test for conflicts
The best way to determine if this behaviour is being caused by a theme and/or plugin is to:
1. Temporarily switch your theme to the Storefront theme.
2. Check if the checkout fields are being loaded. If they are – it is a conflict with your theme. If not, continue to the next step.
3. Temporarily deactivate all plugins except WooCommerce and Square. You can do this manually or use a plugin to help (see below for tools).
4. Try to reproduce the problem again. If the problem is resolved, it is a plugin conflict. To figure out which plugin is causing the problem, continue to the next step.
5. Reactivate your other plugins one by one, testing after each, until you find the one causing conflict.
For more detailed instructions, check out How to test for plugin and theme conflicts:
https://docs.woocommerce.com/document/how-to-test-for-conflicts/
Please let us know how that goes.
Tools to help with troubleshooting
You can clone your site to a staging environment and perform tests without modifying your live site or impacting customers. Many hosts provide staging facilities, so it’s worth checking in with them. It’s also possible to do it using the free WP Staging plugin.