[Bug]: Individual appointments missing from the calendar

⚠️ 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

We have a Nextcloud server in the office that we use to exchange data with our customers.
Since Nextcloud also provides users with a calendar, we use this functionality to coordinate our office appointments. In principle, everyone sees all calendars and can see whether their colleague is available or not. So far so good.

For about a year I have regularly experienced that my calendars are no longer reliably synchronized across all of my devices. I use an iPad, an iPhone, a Macbook and an Imac. The sync of the icloud and Exchange calendars works perfectly, but individual appointments are missing from the nextcloud calendar. I cannot reproduce which device is the source of the trouble.
Only individual calendar entries are missing, not the hole calendar; and it can happen that events entered later are synchronized correctly over all devices, but the entries made in between are missing on the other devices.

Neither me nor our admin can find the error. It's very stressful for me because I'm very busy at work and can't remember all the appointments. And it's very embarrassing to forget appointments.

I would be very happy, if one of you could help me solve the problem. We can also talk about it in more detail via Zoom or Teams. You can reach me at kathy.meiss@igmgh.de or via 0162/7073073

Thank you very much in advance
Yours Kathy

Steps to reproduce

The bug is hard to reproduce, because it is only for some calendar entries and there are 4 devices that are usually syncronized.

Expected behavior

Syncronisation of all Calendar entries on all devices.

Installation method

Community NextcloudPi appliance

Nextcloud Server version

28

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.2

Web server

Apache (supported)

Database engine version

MySQL

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": {
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": {
            "0": "127.0.0.1",
            "1": "192.168.205.5",
            "5": "webshare",
            "7": "nextcloudpi",
            "8": "nextcloudpi.lan",
            "4": "webshare.igmgh.de",
            "11": "213.86.107.186",
            "3": "webshare.igmgh.de",
            "22": "webshare.igmgh.de",
            "": "webshare.igmgh.de",
            "14": "webshare.igmgh.de"
        },
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "28.0.5.1",
        "overwrite.cli.url": "https:\/\/webshare.igmgh.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,
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "memcache.local": "\\OC\\Memcache\\Redis",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "port": 0,
            "timeout": 0,
            "password": "***REMOVED SENSITIVE VALUE***"
        },
        "mail_smtpmode": "smtp",
        "mail_smtpdebug": "true",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "overwriteprotocol": "https",
        "loglevel": 0,
        "log_type": "file",
        "logdateformat": "Y-m-d H:i:s",
        "logtimezone": "Europe\/Berlin",
        "log.condition": {
            "apps": [
                "admin_audit"
            ]
        },
        "maintenance": false,
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "587",
        "skeletondirectory": "\/var\/www\/nextcloud\/core\/skeleton-igmgh",
        "htaccess.RewriteBase": "",
        "jpeg_quality": "60",
        "theme": "",
        "activity_use_cached_mountpoints": true,
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "default_phone_region": "DE",
        "mail_sendmailmode": "smtp",
        "mail_smtpauthtype": "LOGIN",
        "tempdirectory": "\/var\/www\/nextcloud\/data\/tmp",
        "logfile": "\/var\/www\/nextcloud\/data\/nextcloud.log",
        "data-fingerprint": "e136386e30827cce704c594b362ebce7",
        "mail_smtpauth": 1,
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "maintenance_window_start": 22
    }
}

List of activated Apps

Enabled:
  - activity: 2.20.0
  - admin_audit: 1.18.0
  - bruteforcesettings: 2.8.0
  - calendar: 4.7.4
  - circles: 28.0.0
  - cloud_federation_api: 1.11.0
  - comments: 1.18.0
  - contacts: 5.5.3
  - contactsinteraction: 1.9.0
  - dashboard: 7.8.0
  - dav: 1.29.1
  - federatedfilesharing: 1.18.0
  - federation: 1.18.0
  - files: 2.0.0
  - files_pdfviewer: 2.9.0
  - files_reminders: 1.1.0
  - files_sharing: 1.20.0
  - files_trashbin: 1.18.0
  - files_versions: 1.21.0
  - firstrunwizard: 2.17.0
  - groupfolders: 16.0.6
  - logreader: 2.13.0
  - lookup_server_connector: 1.16.0
  - nextcloud_announcements: 1.17.0
  - nextcloudpi: 0.0.2
  - notifications: 2.16.0
  - notify_push: 0.6.11
  - oauth2: 1.16.3
  - password_policy: 1.18.0
  - photos: 2.4.0
  - previewgenerator: 99.99.99
  - privacy: 1.12.0
  - provisioning_api: 1.18.0
  - recommendations: 2.0.0
  - related_resources: 1.3.0
  - serverinfo: 1.18.0
  - settings: 1.10.1
  - sharebymail: 1.18.0
  - support: 1.11.1
  - survey_client: 1.16.0
  - systemtags: 1.18.0
  - text: 3.9.1
  - theming: 2.3.0
  - twofactor_backupcodes: 1.17.0
  - updatenotification: 1.18.0
  - user_status: 1.8.1
  - viewer: 2.2.0
  - weather_status: 1.8.0
  - workflowengine: 2.10.0
Disabled:
  - encryption: 2.16.0
  - files_external: 1.20.0
  - suspicious_login: 6.0.0 (installed 3.2.1)
  - twofactor_totp: 10.0.0-beta.2
  - user_ldap: 1.19.0

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

File to large...please contact our admin at it@igmgh.de

Additional info

No response

The report identifies the calendar and DAV apps but no source file, test, or code entry point, and says the failure cannot be reproduced. Start by obtaining usable Nextcloud logs and a reproducible case across the listed devices; done would require identifying why individual events fail to synchronize and verifying that all calendar entries propagate consistently.