Nextcloud app upgrade abort, claims current installation is not based on docker

it seems like I broke my docker installation.
when I try to:

Starting univention-upgrade. Current UCS version is 4.4-4 errata648

Checking for local repository: none
Checking for package updates: none
Checking for app updates: found

The following apps can be upgraded:

Wekan: Version 3.64 can be upgraded to 4.15
Nextcloud: Version 17.0.2-0 can be upgraded to 18.0.4-0

Here i am wondering why the updater tells me i have nc_17.0.2 installed, when in fact I got 16.06 :face_with_head_bandage:

When i then accept the prompts to do the app-upgrade it fails.

root@magnesium:~# tail /var/log/univention/appcenter.log
6815 actions.upgrade 20-07-05 18:04:02 [CRITICAL]: Unable to upgrade wekan. Aborting…
6815 actions.upgrade.progress 20-07-05 18:04:02 [ DEBUG]: 100
6815 actions.upgrade 20-07-05 18:04:04 [ DEBUG]: Calling upgrade
6815 actions.upgrade.progress 20-07-05 18:04:04 [ DEBUG]: 0
6815 actions.upgrade 20-07-05 18:04:12 [ INFO]: Going to upgrade Nextcloud Hub (18.0.4-0)
6815 actions.upgrade 20-07-05 18:04:12 [CRITICAL]: (shall_not_be_docker_if_discouraged) The application has not been approved to migrate all
existing data. Maybe there is a migration guide:
6815 actions.upgrade 20-07-05 18:04:16 [CRITICAL]: Unable to upgrade nextcloud. Aborting…
6815 actions.upgrade.progress 20-07-05 18:04:16 [ DEBUG]: 100
Some month ago, i had an issue after upgrading the ucs version - docker was not running. I could get it running again - but it seems that I now have to pay the price for my quick fix.

When trying to upgrade within the umc I get:

Ein Fehler trat während der Aktion auf

Die angeforderte Aktion kann nicht durchgeführt werden. Bitte berücksichtigen Sie die Informationen, die unten angegeben sind, um das Problem zu beheben und es erneut zu versuchen.

Nextcloud benutzt eine Container-Technologie, um Sicherheit und Kompatibilität zu erhöhen. Eine Version ohne Container-Technologie ist oder war installiert.

#docker ps

448c8d5ecf57 “/bin/sh -c /usr/sbi…” 7 months ago Up 21 minutes>80/tcp vigilant_yalow
9c9758c0f139 “node /build/main.js” 9 months ago Restarting (1) 43 seconds ago wekan-app
6d0c5a54b3ee “docker-entrypoint.s…” 9 months ago Restarting (14) 28 seconds ago wekan-db

anyone how has at least an idea where i can start to look?
Kind regards from Kiel
THX in advance