No notification emails are sent if mentioned in file comments

⚠️ 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 (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

No notification is sent when a comment on a file is posted with a personal notification.

In the activity (web frontend) the comment is mentioned. Thus, it is detected correctly by the server. Only the immediate sending of mails is not done.

The delayed sending of the mails is not affected. Other mails can also be sent. So, the problem is not related to the mailing system.

Steps to reproduce

1. Set the personal notifications to send mails on comments on files.
   
2. Also, set the notifications for email reminders for unhandled notifications
   
3. Prepare another account A and add a shared file.
4. Put a comment as user A on the shared file with a mention to the main account (with @...).
5. Have a look at the mails now and in one day

Expected behavior

The mail is immediately sent out when Nextcloud is configured to send out the mail upon comments.

Installation method

Official docker container

Operating system

Archlinux as host OS, official docker container as guest container

PHP engine version

8.0

Web server

Apache

Database engine version

MariaDB

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

Unsure, I think it was the fresh installation from docker hub without migrations.

Are you using the Nextcloud Server Encryption module?

No encryption used

What user-backends are you using?

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

Configuration report

{
    "system": {
        "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
            }
        ],
        "memcache.distributed": "\\OC\\Memcache\\Redis",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "***REMOVED SENSITIVE VALUE***",
            "password": "***REMOVED SENSITIVE VALUE***",
            "port": 6379
        },
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "cloud.tsc-vfl.de"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "24.0.1.1",
        "overwrite.cli.url": "https:\/\/cloud.tsc-vfl.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,
        "app_install_overwrite": [
            "twofactor_admin",
            "files_texteditor"
        ],
        "maintenance": false,
        "mail_smtpmode": "smtp",
        "mail_smtpsecure": "tls",
        "mail_sendmailmode": "smtp",
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpauth": 1,
        "mail_smtpauthtype": "PLAIN",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpport": "587",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***"
    }
}

List of activated Apps

Enabled:
  - accessibility: 1.10.0
  - activity: 2.16.0
  - appointments: 1.12.6
  - apporder: 0.15.0
  - bruteforcesettings: 2.4.0
  - calendar: 3.3.2
  - checksum: 1.1.4
  - circles: 24.0.0
  - cloud_federation_api: 1.7.0
  - collectives: 1.2.0
  - comments: 1.14.0
  - contacts: 4.1.1
  - contactsinteraction: 1.5.0
  - dav: 1.22.0
  - deck: 1.7.1
  - external: 4.0.0
  - federatedfilesharing: 1.14.0
  - federation: 1.14.0
  - files: 1.19.0
  - files_antivirus: 3.3.0
  - files_downloadactivity: 1.13.0
  - files_linkeditor: 1.1.10
  - files_markdown: 2.3.6
  - files_mindmap: 0.0.26
  - files_pdfviewer: 2.5.0
  - files_rightclick: 1.3.0
  - files_sharing: 1.16.2
  - files_texteditor: 2.14.0
  - files_trashbin: 1.14.0
  - files_versions: 1.17.0
  - files_videoplayer: 1.13.0
  - firstrunwizard: 2.13.0
  - forms: 2.5.1
  - groupfolders: 12.0.0
  - groupquota: 0.1.8
  - impersonate: 1.11.0
  - integration_google: 1.0.6
  - logreader: 2.9.0
  - lookup_server_connector: 1.12.0
  - mail: 1.13.4
  - metadata: 0.16.0
  - nextcloud_announcements: 1.13.0
  - notes: 4.3.1
  - notifications: 2.12.0
  - oauth2: 1.12.0
  - oidc_login: 2.3.2
  - password_policy: 1.14.0
  - photos: 1.6.0
  - polls: 3.6.1
  - privacy: 1.8.0
  - provisioning_api: 1.14.0
  - quota_warning: 1.14.0
  - recommendations: 1.3.0
  - richdocuments: 6.1.0
  - serverinfo: 1.14.0
  - settings: 1.6.0
  - sharebymail: 1.14.0
  - sociallogin: 4.15.3
  - spreed: 14.0.2
  - support: 1.7.0
  - survey_client: 1.12.0
  - systemtags: 1.14.0
  - tasks: 0.14.4
  - text: 3.5.1
  - theming: 1.15.0
  - transfer: 0.5.1
  - twofactor_backupcodes: 1.13.0
  - twofactor_email: 2.4.0
  - twofactor_nextcloud_notification: 3.4.0
  - twofactor_totp: 6.4.0
  - twofactor_webauthn: 0.3.1
  - updatenotification: 1.14.0
  - user_status: 1.4.0
  - user_usage_report: 1.8.0
  - viewer: 1.8.0
  - workflowengine: 2.6.0
Disabled:
  - admin_audit
  - dashboard: 7.4.0
  - encryption
  - files_external
  - twofactor_u2f
  - user_ldap
  - weather_status: 1.4.0

Nextcloud Signing status

No errors have been found.

Nextcloud Logs

Log in gist (large file of >50MB)

Additional info

I am using the official docker image under an Archlinux host.

I am unsure if this problem is related to the NC server or to a dedicated app. I asked for help on the forum but did not get any answer so far.

I tried to search for this problem but did not find anything useful so far. If it is in fact a duplicate, please be kind and direct me to the correct location.

Here are some information extracted from the server directly: https://cloud.tsc-vfl.de/index.php/s/DGM3FqPRaQmWEJy

Regarding the Nextcloud logs, at what point in time do you need the logs. At the time of the mentioning (missing mail) or later? Currently, the file is roughly 100MB in size and I cannot create a gist from it for some reason.

No source files or tests are named in the report. Start by tracing the file-comment mention notification path and compare immediate email delivery with the delayed reminder flow using the reproduction steps; done means an immediate email is sent for a mentioned user while delayed reminders and other mail remain unaffected.