Https://scan.nextcloud.com/ - Scan failed! The scan for the specified domain failed

Dear all,

till a few weeks the security scan worked for our NC instance. Nowadays the message " Scan failed! The scan for the specified domain failed. Either no Nextcloud or ownCloud can be found there or you tried to scan too many servers." appears immediately after a click on the scan button. The host is only available through port 443/https.

Could it be that the host is blocked as we had the security scan as part of our Nagios monitoring system. Maybe Nagios checked too often?

(A scan on securityheaders.com is working fine.)

Thanks in advance.