We believe that the issue might be due to the removal/ disabling of the country fields from the billing or shipping sections. Please be informed that when you provide validation for the state field or zip code field in any section, it is mandatory to have an active country field. You can resolve this issue by creating the billing_country or shipping_country field.
If you don’t have a country field then please verify after adding it.
Further, if you are selling your products only to few countries and you don’t want to let the customer select other countries from the checkout page. Instead of deleting the default country field, you can achieve your requirement by navigating to WooCommerce>>Settings>>General>>General options>>Selling location(s), select the option Sell to specific countries and select the Countries as per your requirement.
Please note that it is recommended not to remove or override the default WooCommerce fields.
Thank you!