I have the this started after upgrading from CE2.1.7 to CE2.1.8, Currently my version in CE 2.1.9 but still getting the same issue.
Default Country Spain and locale United Kingdom for now.
=> Screenshot :
It seems to be locale specific issue. try to create same rule after setting english locale . for reference you may check this issue on git https://github.com/magento/magento2/issues/10686