Azure Web Application Firewall for Azure Front Door Service now has a match details field in the logs to provide insights on why a request triggered a Web Application Firewall rule. In addition, you can facilitate further analysis by embedding the unique reference string in a Web Application Firewall custom response message to link the request to a specific entry in the Azure Front Door Service and Web Application Firewall logs.
For more details, read about Web Application Firewall monitoring and Web Application Firewall custom response.