Cannot share calendar with new user (nor add them as attendees)

Steps to reproduce

1. Create a new calendar
2. Attempt to share it with a specifc new user
3. Their username doesn't appear and so it's impossible to share the calendar with them.

Works fine for all other users, just not this new one. Can share files, boards etc with this new user fine, just not calendars. Also unable to add them as an attendee to the events.

Expected behaviour

I expect to be able to share calendar and events with all users.

Actual behaviour

I cannot share calendars nor events with one specific new users. I can share anything else (files, talk, desk, etc) with them, just not calendars nor events.

Calendar app version

3.4.2

CalDAV-clients used

n/a

Browser

Tested on Firefox 103.0 (64-bit) and Chromium 104.0.5112.79 (Official Build) snap (64-bit)

Client operating system

Ubuntu 20.04

Server operating system

Ubuntu 18.04

Web server

No response

Database engine version

No response

PHP engine version

No response

Nextcloud version

24.0.3

Updated from an older installed version or fresh install

Updated from an older version

List of activated apps

Enabled:
  - accessibility: 1.10.0
  - activity: 2.16.0
  - calendar: 3.4.2
  - circles: 24.0.0
  - cloud_federation_api: 1.7.0
  - comments: 1.14.0
  - contacts: 4.2.0
  - contactsinteraction: 1.5.0
  - dashboard: 7.4.0
  - dav: 1.22.0
  - deck: 1.7.1
  - federatedfilesharing: 1.14.0
  - federation: 1.14.0
  - files: 1.19.0
  - files_pdfviewer: 2.5.0
  - files_rightclick: 1.3.0
  - files_sharing: 1.16.2
  - files_trashbin: 1.14.0
  - files_versions: 1.17.0
  - files_videoplayer: 1.13.0
  - firstrunwizard: 2.13.0
  - logreader: 2.9.0
  - lookup_server_connector: 1.12.0
  - nextcloud_announcements: 1.13.0
  - notifications: 2.12.0
  - oauth2: 1.12.0
  - onlyoffice: 7.5.4
  - password_policy: 1.14.0
  - photos: 1.6.0
  - privacy: 1.8.0
  - provisioning_api: 1.14.0
  - recommendations: 1.3.0
  - serverinfo: 1.14.0
  - settings: 1.6.0
  - sharebymail: 1.14.0
  - spreed: 14.0.3
  - support: 1.7.0
  - survey_client: 1.12.0
  - systemtags: 1.14.0
  - text: 3.5.1
  - theming: 1.15.0
  - twofactor_backupcodes: 1.13.0
  - updatenotification: 1.14.0
  - user_ldap: 1.14.1
  - user_status: 1.4.0
  - viewer: 1.8.0
  - weather_status: 1.4.0
  - workflowengine: 2.6.0
Disabled:
  - admin_audit
  - encryption
  - files_external

Nextcloud configuration

{
    "system": {
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "office.bettermedia.uk"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "pgsql",
        "version": "24.0.3.2",
        "overwrite.cli.url": "https:\/\/office.bettermedia.uk\/",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "default_phone_region": "US",
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "forcessl": "1",
        "mail_smtpmode": "smtp",
        "mail_smtpauth": 1,
        "mail_sendmailmode": "smtp",
        "mail_smtpauthtype": "LOGIN",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "2525",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "overwritehost": "office.bettermedia.uk",
        "overwriteprotocol": "https",
        "updatechecker": false,
        "updater.release.channel": "cloudron",
        "logfile": "\/dev\/stderr",
        "loglevel": "3",
        "debug": false,
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": "6379",
            "password": "***REMOVED SENSITIVE VALUE***"
        },
        "memcache.local": "\\OC\\Memcache\\Redis",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "integrity.check.disabled": true,
        "htaccess.RewriteBase": "\/",
        "simpleSignUpLink.shown": false,
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "ldapProviderFactory": "OCA\\User_LDAP\\LDAPProviderFactory",
        "mail_smtpsecure": "",
        "maintenance": false
    }
}

Web server error log

No response

Log file

No response

Browser log

No response

Additional info

No response

Reproduce the issue in the Calendar app using the listed steps with a newly created user, checking both calendar sharing and event attendees. Start by tracing the user-selection and sharing flows in the calendar app; no source files or tests are identified in the report. Done means the new user appears in both flows while existing sharing behavior remains intact.