Hi,
I installed a new Nextcloud instance from scratch. And took it in production yesterday.
It replaces the old Nextcloud, with same hostname, ip adress etc. The old Nextcloud is taken down en the new one is up since yesterday!
Everything is working fine. Except: the security check from nextcloud also (Owncloud check) gives me a Failed to scan.
The server is reachable from outside. Any ideas?
There is an issue with the scanner right now. So nothing about your system itself.
I take it you tried this:
What are the noted ‘failings’? You should easily get an ‘A’ for NC version 15.
Oh, I just tried the service and it is temporarily down with this 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."
So if you are seeing this, it’s NOT your Nextcloud instance at fault, it’s their security scan service. 
I also get a fail on owncloud security check, where another nextcloud instance of a friend of my passes.
I checked again, and now I get a pass!