Yes, I can reproduce your issue, don’t have a solution.
Trying with https://nc.c-rieger.de/login makes a new scan and ends with no Installation found error…
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.
Think nextcloud have to delete the scan from 17/02/20 out of their cache…
@LukasReschke ???