Your version of WooCommerce Checkout Manager has a bug.
Setting the State field to “mandatory” seems to serve no purpose except to break stores. If set to mandatory, it’s required for all countries, even those without states - except the state field doesn’t even appear for these countries. So this blocks the customer from checking out.
If NOT set to mandatory, it’s still made mandatory anyway for countries that require a state.
Not sure what the point is of having the mandatory option here.