File retention not working


I’m running nextcloud 18.0.4 as docker image on top of Debian 9 server behind a proxy.
We are facing issues with file retention module.
We were able to configure the automatic tagging for any file uploaded by “test” group: Each file that is uploaded by a member of test group gets the “retention” tag.
We have then configured a retention rule to delete any file with that tag after 1 day. However we still have the files there, nothing was deleted.
We have tested that on both local and LDAP users, still the same issue.

Anyone faced this issue before?

Update : I’ve enabled Cron as background jobs runner using the UI and now I have issues saying : Last job execution ran 1 hour ago. Something seems wrong.

I’ve installed java on my debian machine to fix this, but still having problems on my machine saying :
Could not open input file: /var/lib/docker/volumes/nextcloud/_data/cron.php

My crontab configuration file looks like this :
*/5 * * * * php -f /var/lib/docker/volumes/nextcloud/_data/cron.php