Old user data is not removed.
I'd like to highlight this issue, so it's easier to find for others. The
oc_cards table is used for finding people to share files with.
Old user data might have been accumulated in the
oc_cards table. This table might have been filled by the LDAP app, which I have also experimented with.
oc_cards table contains no really important data, it should be safe to empty it. That goes like this:
mysqldump --no-data nextcloud oc_cards > oc_cards.sql mysql nextcloud < oc_cards.sql