[Bug]: User accounts show up multiple times in Contacts

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

Some User Accounts show up multiple times in the Contacts list.
Most of my Users show up as just one singular entry, with all their registered info.
But one of them has two entries, where the second entry only shows a Federated Cloud ID.
One of my users has three entries; one with all registered info, one extra with just their E-Mail address, one with literally no info at all.
None of those entries can seemingly be deleted.

Steps to reproduce

not sure what caused this, no idea how to reproduce.

Expected behavior

no duplicates in contacts list

Nextcloud Server version

29

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.3

Web server

Apache (supported)

Database engine version

MariaDB

Is this bug present after an update or on a fresh install?

Fresh Nextcloud Server install

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

{
    "system": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "redacted.kaleidox.de"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "29.0.4.1",
        "overwrite.cli.url": "http:\/\/warmulla.kaleidox.de",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "default_language": "de",
        "default_locale": "de_DE",
        "force_language": "de",
        "force_locale": "de_DE",
        "app_install_overwrite": [
            "files_trackdownloads",
            "checksum_api",
            "admin_notifications",
            "files_markdown"
        ],
        "defaultapp": ""
    }
}
Cannot write into "config" directory!
This can usually be fixed by giving the web server write access to the config directory.

But, if you prefer to keep config.php file read only, set the option "config_is_read_only" to true in it.
See https://docs.nextcloud.com/server/29/go.php?to=admin-config
{"reqId":"fBBZy3M3YkE6d93yNQHN","level":3,"time":"2024-08-30T15:54:37+00:00","remoteAddr":"","user":"--","app":"PHP","method":"","url":"--","message":"fopen(/var/www/nextcloud/config/config.php): Failed to open stream: Permission denied at /var/www/nextcloud/lib/private/Config.php#221","userAgent":"--","version":"","data":{"app":"PHP"}}
Cannot write into "config" directory!
This can usually be fixed by giving the web server write access to the config directory.

But, if you prefer to keep config.php file read only, set the option "config_is_read_only" to true in it.
See https://docs.nextcloud.com/server/29/go.php?to=admin-config
{"reqId":"Du2ucfKaBycOOHMFrmbt","level":3,"time":"2024-08-30T15:54:37+00:00","remoteAddr":"","user":"--","app":"PHP","method":"","url":"--","message":"fopen(/var/www/nextcloud/config/config.php): Failed to open stream: Permission denied at /var/www/nextcloud/lib/private/Config.php#221","userAgent":"--","version":"","data":{"app":"PHP"}}

List of activated Apps

Enabled:
  - activity: 2.21.1
  - approval: 1.3.0
  - calendar: 4.7.15
  - cfg_share_links: 5.1.1
  - circles: 29.0.0-dev
  - cloud_federation_api: 1.12.0
  - comments: 1.19.0
  - contacts: 6.0.0
  - contactsinteraction: 1.10.0
  - dashboard: 7.9.0
  - dav: 1.30.1
  - drawio: 3.0.2
  - federatedfilesharing: 1.19.0
  - federation: 1.19.0
  - files: 2.1.0
  - files_downloadactivity: 1.17.0
  - files_downloadlimit: 2.0.0
  - files_markdown: 2.4.1
  - files_pdfviewer: 2.10.0
  - files_reminders: 1.2.0
  - files_sharing: 1.21.0
  - files_trackdownloads: 1.11.0
  - files_trashbin: 1.19.0
  - firstrunwizard: 2.18.0
  - groupfolders: 17.0.1
  - guests: 3.1.0
  - logreader: 2.14.0
  - lookup_server_connector: 1.17.0
  - mail: 3.7.7
  - nextcloud_announcements: 1.18.0
  - notes: 4.10.1
  - notifications: 2.17.0
  - oauth2: 1.17.0
  - password_policy: 1.19.0
  - passwords: 2024.7.10
  - privacy: 1.13.0
  - provisioning_api: 1.19.0
  - related_resources: 1.4.0
  - richdocuments: 8.4.4
  - richdocumentscode: 24.4.502
  - serverinfo: 1.19.0
  - settings: 1.12.0
  - sharebymail: 1.19.0
  - spreed: 19.0.7
  - support: 1.12.0
  - systemtags: 1.19.0
  - tasks: 0.16.0
  - text: 3.10.1
  - theming: 2.4.0
  - timemanager: 0.3.15
  - twofactor_backupcodes: 1.18.0
  - updatenotification: 1.19.1
  - user_status: 1.9.0
  - viewer: 2.3.0
  - workflowengine: 2.11.0
Disabled:
  - admin_audit: 1.19.0
  - admin_notifications: 1.0.2 (installed 1.0.2)
  - bruteforcesettings: 2.9.0
  - cadviewer: 9.71.1 (installed 9.71.1)
  - encryption: 2.17.0
  - files_external: 1.21.0
  - files_versions: 1.22.0 (installed 1.22.0)
  - integration_collaboard: 1.0.8 (installed 1.0.8)
  - integration_github: 2.0.7 (installed 2.0.7)
  - integration_mastodon: 2.0.6 (installed 2.0.6)
  - photos: 2.5.0 (installed 2.5.0)
  - recommendations: 2.1.0 (installed 2.1.0)
  - sip_trip_phone: 1.1.5 (installed 1.1.5)
  - survey_client: 1.17.0 (installed 1.17.0)
  - suspicious_login: 7.0.0
  - twofactor_totp: 11.0.0-dev
  - user_ldap: 1.20.0
  - weather_status: 1.9.0 (installed 1.9.0)
Cannot write into "config" directory!
This can usually be fixed by giving the web server write access to the config directory.

But, if you prefer to keep config.php file read only, set the option "config_is_read_only" to true in it.
See https://docs.nextcloud.com/server/29/go.php?to=admin-config
{"reqId":"dVH0TZjdCTdBY36t3dpk","level":3,"time":"2024-08-30T15:55:03+00:00","remoteAddr":"","user":"--","app":"PHP","method":"","url":"--","message":"fopen(/var/www/nextcloud/config/config.php): Failed to open stream: Permission denied at /var/www/nextcloud/lib/private/Config.php#221","userAgent":"--","version":"","data":{"app":"PHP"}}
Cannot write into "config" directory!
This can usually be fixed by giving the web server write access to the config directory.

But, if you prefer to keep config.php file read only, set the option "config_is_read_only" to true in it.
See https://docs.nextcloud.com/server/29/go.php?to=admin-config
{"reqId":"OHeKNT7mJh7GEEaikC46","level":3,"time":"2024-08-30T15:55:03+00:00","remoteAddr":"","user":"--","app":"PHP","method":"","url":"--","message":"fopen(/var/www/nextcloud/config/config.php): Failed to open stream: Permission denied at /var/www/nextcloud/lib/private/Config.php#221","userAgent":"--","version":"","data":{"app":"PHP"}}

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

too much sensitive data inside. this is a company instance.

Additional info

note that the OCC commands have been executed from a user that does not have access to the nextcloud directories; "read only" reports may be inaccurate.