Once an active site is removed from the Cloud WAF service, a copy of the site's configuration is still kept for 24 hours on PoPs across the network.
This is by design so as to not disrupt incoming traffic to the site and to allow the new DNS records to propagate world-wide.
It is important to note that if the same domain/site is re-added to the Cloud WAF service within a period of 24 hours since its removal, traffic will not be passed to the origin server.
Rather Cloud WAF Error Code 23 will be presented to users since essentially the PoPs detect "duplicate sites with the same hostname exist".
Therefore, in order to avoid any inconveniences, we highly recommend waiting at least 24 hours before re-adding a previously deleted site/domain.