So my theory worked for me at least. Looks like openproject use an old 4.3-5 version in their container image. Running the manual install of the ucs5 key as per the workaround inside the container allowed the update to work.
I’m now getting offered the 5.0 release upgrade too (although I’m not ready to do that) so hopefully that clears the way for you too.
My Nextcloud container wasn’t affected by this for example as it looks like they use an ubuntu base image instead of UCS base image.
Cheers.
7396 actions.upgrade.container.4ed7 21-07-26 10:18:12 [ INFO]: ==============
7396 actions.upgrade.container.4ed7 21-07-26 10:18:12 [ INFO]: The openproject package provides an installer. Please run the following command to finish the installation:
7396 actions.upgrade.container.4ed7 21-07-26 10:18:12 [ INFO]: sudo openproject configure
7396 actions.upgrade.container.4ed7 21-07-26 10:18:12 [ INFO]: ==============
7396 actions.upgrade.container.4ed7 21-07-26 10:18:13 [ INFO]:
7396 actions.upgrade.container.4ed7 21-07-26 10:18:13 [ INFO]: Starting univention-upgrade. Current UCS version is 4.3-5 errata682
7396 actions.upgrade.container.4ed7 21-07-26 10:18:13 [ INFO]:
7396 actions.upgrade.container.4ed7 21-07-26 10:18:13 [ INFO]: Checking for local repository: none
7396 actions.upgrade.container.4ed7 21-07-26 10:19:35 [ INFO]: Checking for package updates: none
7396 actions.upgrade.container.4ed7 21-07-26 10:19:35 [ INFO]: Checking for app updates: skipped
7396 actions.upgrade.container.4ed7 21-07-26 10:19:45 [ INFO]: Checking for release updates: none
7396 actions.upgrade.container.4ed7 21-07-26 10:19:45 [ WARNING]: The update to UCS 4.4 is blocked because the component 'openproject_20210705143001' is marked as required.