download.opensuse.org appears to be back online, but for some reason the repository isn't working as expected:
$ sudo apt-get update Ign:17 http://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Debian_9.0 Contents (deb) Reading package lists... W: The repository 'http://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Debian_9.0 Release' does not have a Release file. E: Failed to fetch http://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Debian_9.0/Packages Connection failed E: Some index files failed to download. They have been ignored, or old ones used instead.
Maybe there's an openSUSE download server maintenance in progress?