[Bug]: All root folders renamed to "<folder_name> 2" for a single user

⚠️ This issue respects the following points: ⚠️

• This is not a troubleshooting question, general support matter, or webserver/proxy problem, but likely a bug (if unsure, ask the Community Help Forum).
• This issue is not already reported on Github OR solved at the Community Help Forum (I've searched!).
• I'm using a maintained major version of Nextcloud Server and tested against the latest patch level. (Supported major versions and current patch levels).
• I agree to follow Nextcloud's Code of Conduct.
• I've tried my best to provide clear reproduction steps that someone unfamiliar with this bug could use to reproduce it.

Bug description

A week ago (around when I upgraded to 34.0.3) some random files started re-creating (may be a benign re-synchronization of some folders) and then yesterday (13 hours ago as I write) all folders in the root renamed to "<folder_name> 2" for one of the users. The desktop Mac client started recreating all folder structure without uploading anything. Maybe it just did not have enough time to start uploading until I stopped it.

Steps to reproduce

1. Upgrade to 34.0.3
2. Wait for a week
3. Start noticing the issues
   (Sorry, there is really nothing else I can provide as StR)

Expected behavior

No folders are renamed.

Nextcloud Server version

34

Operating system

Debian/Ubuntu

PHP engine version

None

Web server

None

Database engine version

None

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

None

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": {
        "htaccess.RewriteBase": "\/",
        "memcache.local": "\\OC\\Memcache\\APCu",
        "apps_paths": [
            {
                "path": "\/var\/www\/html\/apps",
                "url": "\/apps",
                "writable": false
            },
            {
                "path": "\/var\/www\/html\/custom_apps",
                "url": "\/custom_apps",
                "writable": true
            }
        ],
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "192.168.0.136:8666",
            "***MANUALLY REMOVED SENSITIVE VALUE***"
        ],
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "overwrite.cli.url": "***MANUALLY REMOVED SENSITIVE VALUE***",
        "overwriteprotocol": "https",
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "34.0.3.2",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "3306",
        "dbtableprefix": "oc_",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "loglevel": 0,
        "maintenance": false,
        "theme": "",
        "upgrade.disable-web": true,
        "maintenance_window_start": 1,
        "app_install_overwrite": []
    }
}
$ {
    "system": {
        "htaccess.RewriteBase": "\/",
        "memcache.local": "\\OC\\Memcache\\APCu",
        "apps_paths": [
            {
                "path": "\/var\/www\/html\/apps",
                "url": "\/apps",
                "writable": false
            },
            {
                "path": "\/var\/www\/html\/custom_apps",
                "url": "\/custom_apps",
                "writable": true
            }
        ],
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "192.168.0.136:8666",
            "***MANUALLY REMOVED SENSITIVE VALUE***"
        ],
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "overwrite.cli.url": "***MANUALLY REMOVED SENSITIVE VALUE***",
        "overwriteprotocol": "https",
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "34.0.3.2",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "3306",
        "dbtableprefix": "oc_",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "loglevel": 0,
        "maintenance": false,
        "theme": "",
        "upgrade.disable-web": true,
        "maintenance_window_start": 1,
        "app_install_overwrite": []
    }
}

List of activated Apps

$ Enabled:
  - activity: 7.0.0
  - appstore: 1.0.0
  - bruteforcesettings: 7.0.0
  - circles: 34.0.0
  - cloud_federation_api: 1.18.0
  - comments: 1.24.0
  - contactsinteraction: 1.15.0
  - dashboard: 7.14.0
  - dav: 1.40.0
  - federatedfilesharing: 1.24.0
  - federation: 1.24.0
  - files: 2.6.0
  - files_downloadlimit: 5.2.0
  - files_external: 1.26.0
  - files_lock: 34.0.1
  - files_pdfviewer: 7.0.0-dev.0
  - files_reminders: 1.7.0
  - files_sharing: 1.26.0
  - files_trashbin: 1.24.0
  - files_versions: 1.27.0
  - firstrunwizard: 7.0.0-dev.0
  - logreader: 7.0.0
  - lookup_server_connector: 1.22.0
  - nextcloud_announcements: 6.0.0
  - notifications: 7.0.0-dev.1
  - oauth2: 1.22.0
  - office: 1.0.0
  - password_policy: 6.0.0-dev.0
  - photos: 7.0.0
  - privacy: 6.0.0-dev.1
  - profile: 1.3.0
  - provisioning_api: 1.24.0
  - recommendations: 7.0.0
  - related_resources: 5.0.0-dev.0
  - serverinfo: 6.0.0
  - settings: 1.17.0
  - sharebymail: 1.24.0
  - support: 6.0.0
  - survey_client: 6.0.0-dev.0
  - systemtags: 1.24.0
  - text: 8.0.0
  - theming: 2.9.0
  - twofactor_backupcodes: 1.23.0
  - twofactor_totp: 16.0.0
  - updatenotification: 1.24.0
  - user_status: 1.14.0
  - viewer: 7.0.0-dev.0
  - weather_status: 1.14.0
  - webhook_listeners: 1.6.0
  - workflowengine: 2.16.0
Disabled:
  - admin_audit: 1.24.0
  - app_api: 34.0.0 (installed 32.0.0)
  - encryption: 2.22.0
  - suspicious_login: 12.0.0-dev.0
  - twofactor_nextcloud_notification: 8.0.0
  - user_ldap: 1.25.0

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

Could not recover the log on the time of occurrence

Additional info

Host OS: Unraid 7.3.1 running Docker with Nextcloud. DB is mariadb:11.8.3-ubi docker instance.

No source file, entry point, or test is identified in the report. Start by reproducing the upgrade and desktop-client sequence while collecting server and client logs; done means identifying the cause of the root-folder renames and adding a regression test that prevents them.