Apt update && apt upgrade fails - 404 for Ubuntu_16.04/./all/owncloud_10.0.0-1.1_all.deb

Please help us by providing the following info. Before posting please also check the pinned "Known issues" threads and make sure that you're running the latest available version for your oC release: https://owncloud.org/changelog/

Steps to reproduce
1.apt update
2.apt upgrade
3.

Expected behaviour
I'd expect the packages to be found, downloaded, and applied.

Actual behaviour
Instead I get

root@cloud-ourspace-io:~# cat cloud /etc/apt/sources.list.d/owncloud.list
cat: cloud: No such file or directory
deb https://download.owncloud.org/download/repositories/stable/Ubuntu_16.04/ /
root@cloud-ourspace-io:~#
root@cloud-ourspace-io:~#
root@cloud-ourspace-io:~# apt update
Hit:1 http://archive.ubuntu.com/ubuntu xenial InRelease
Hit:2 http://security.ubuntu.com/ubuntu xenial-security InRelease
Hit:3 http://archive.ubuntu.com/ubuntu xenial-updates InRelease
Hit:4 http://archive.ubuntu.com/ubuntu xenial-backports InRelease
Ign:5 https://download.owncloud.org/download/repositories/stable/Ubuntu_16.04 InRelease
Hit:6 https://download.owncloud.org/download/repositories/stable/Ubuntu_16.04 Release
Reading package lists... Done
Building dependency tree
Reading state information... Done
34 packages can be upgraded. Run 'apt list --upgradable' to see them.
root@cloud-ourspace-io:~# apt full-upgrade -y
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following package was automatically installed and is no longer required:
snap-confine
Use 'apt autoremove' to remove it.
The following packages will be upgraded:
apt apt-transport-https apt-utils cloud-init dnsmasq-base dpkg libapt-inst2.0 libapt-pkg5.0 libgtk-3-0 libgtk-3-bin libgtk-3-common libpam-systemd libpci3 libsane libsane-common
libsystemd0 libudev1 makedev owncloud owncloud-deps-php7.0 owncloud-files pciutils python3-software-properties python3-update-manager snap-confine snapd
software-properties-common systemd systemd-sysv ubuntu-core-launcher udev update-manager-core update-notifier-common wget
34 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 27.8 MB/53.3 MB of archives.
After this operation, 43.3 MB of additional disk space will be used.
Err:1 https://download.owncloud.org/download/repositories/stable/Ubuntu_16.04 owncloud 10.0.0-1.1
404 Not Found
Err:2 https://download.owncloud.org/download/repositories/stable/Ubuntu_16.04 owncloud-files 10.0.0-1.1
404 Not Found
Err:3 https://download.owncloud.org/download/repositories/stable/Ubuntu_16.04 owncloud-deps-php7.0 10.0.0-1.1
404 Not Found
E: Failed to fetch https://download.owncloud.org/download/repositories/stable/Ubuntu_16.04/./all/owncloud_10.0.0-1.1_all.deb 404 Not Found

E: Failed to fetch https://download.owncloud.org/download/repositories/stable/Ubuntu_16.04/./all/owncloud-files_10.0.0-1.1_all.deb 404 Not Found

E: Failed to fetch https://download.owncloud.org/download/repositories/stable/Ubuntu_16.04/./all/owncloud-deps-php7.0_10.0.0-1.1_all.deb 404 Not Found

E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?
root@cloud-ourspace-io:~#

Server configuration
Operating system: Ubuntu
Web server: apache
Database: mysql
PHP version: 7.0
ownCloud version (see ownCloud admin page): owncloud/now 9.1.4-2.1 all [installed,upgradable to: 10.0.0-1.1]
Updated from an older ownCloud or fresh install: current version is fresh install

If I presume that https://download.owncloud.org has mirrors behind it, then clearly one (or more) is not up-to-date and needs to fixed.

Please report such issues always directly to the repository maintainer reachable via https://github.com/owncloud/core/issues

In this case your issue might match the one already reported here: