importing calendar (as abo) works from one site, but not from the other site; workound exists

Steps to reproduce

1. create "new subscription from link (readonly)" and put in dedicated subscription URL (in my case it's german calendar, but that doesn't matter):

1a) URL which is working well: https://www.feiertage-deutschland.de/kalender-download/ics/feiertage-deutschland.ics
you see new calendar entries, when displaying this calendar

1b) URL which is not working and importing: https://www.xn--das-feriados-sfb.com/de/feiertage/europa/deutschland/de.de.ics
you see no new calender entries
export of that calender is empty (only header area is in) see: exported(de.de).ics.txt
there is no error message on import

I've also added the downloaded origin calender file here for comparision
de.de.ics.txt

Expected behavior

the calendar file is imported successfully

Actual behavior

see above

Calendar app version

6.2.4

CalDAV-clients used

No response

Browser

No response

Client operating system

No response

Server operating system

Ubuntu 24.04

Web server

Nginx

Database engine version

PostgreSQL

PHP engine version

PHP 8.4

Nextcloud version

33.0.3

Updated from an older installed version or fresh install

Updated from an older version

List of activated apps

Enabled:
  - activity: 6.0.0
  - bruteforcesettings: 6.0.0
  - calendar: 6.2.4
  - circles: 33.0.0
  - cloud_federation_api: 1.17.0
  - contacts: 8.4.5
  - contactsinteraction: 1.14.1
  - dashboard: 7.13.0
  - dashlink: 1.2.1
  - dav: 1.36.0
  - federatedfilesharing: 1.23.0
  - files: 2.5.0
  - files_downloadlimit: 5.1.0
  - files_pdfviewer: 6.0.0
  - files_reminders: 1.6.0
  - files_sharing: 1.25.2
  - files_trashbin: 1.23.0
  - files_versions: 1.26.0
  - logreader: 6.0.0
  - lookup_server_connector: 1.21.0
  - mail: 5.7.14
  - notes: 5.0.0
  - notifications: 6.0.0
  - oauth2: 1.21.0
  - password_policy: 5.0.0
  - privacy: 5.0.0
  - profile: 1.2.0
  - provisioning_api: 1.23.0
  - serverinfo: 5.0.0
  - settings: 1.16.0
  - sharebymail: 1.23.0
  - spreed: 23.0.4
  - tasks: 0.17.1
  - text: 7.0.1
  - theming: 2.8.0
  - twofactor_backupcodes: 1.22.0
  - twofactor_totp: 15.0.0
  - updatenotification: 1.23.0
  - user_status: 1.13.0
  - viewer: 6.0.0
  - workflowengine: 2.15.0
Disabled:
  - admin_audit: 1.23.0
  - app_api: 33.0.0 (installed 33.0.0)
  - comments: 1.23.0 (installed 1.23.0)
  - encryption: 2.21.0
  - federation: 1.23.0 (installed 1.23.0)
  - files_external: 1.25.1
  - firstrunwizard: 6.0.0 (installed 6.0.0-dev.0)
  - nextcloud_announcements: 5.0.0 (installed 5.0.0)
  - photos: 6.0.0 (installed 6.0.0-dev.0)
  - recommendations: 6.0.0 (installed 6.0.0-dev.0)
  - related_resources: 4.0.0 (installed 4.0.0-dev.0)
  - support: 5.0.0 (installed 5.0.0)
  - survey_client: 5.0.0 (installed 5.0.0-dev.0)
  - suspicious_login: 11.0.0
  - systemtags: 1.23.0 (installed 1.23.0)
  - testing: 1.23.0
  - twofactor_nextcloud_notification: 7.0.0
  - user_ldap: 1.24.0
  - weather_status: 1.13.0 (installed 1.13.0)
  - webhook_listeners: 1.5.0 (installed 1.5.0)

Nextcloud configuration

{
    "system": {
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "nc.klare-beratung.de"
        ],
        "dbtype": "pgsql",
        "version": "33.0.3.2",
        "overwrite.cli.url": "https:\/\/nc.klare-beratung.de",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "memcache.local": "\\OC\\Memcache\\APCu",
        "filelocking.enabled": true,
        "memcache.locking": "\\OC\\Memcache\\APCu",
        "upgrade.disable-web": true,
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpmode": "smtp",
        "mail_sendmailmode": "smtp",
        "mail_smtpstreamoptions": {
            "ssl": {
                "allow_self_signed": false,
                "verify_peer": true,
                "verify_peer_name": true
            }
        },
        "maintenance": false,
        "mail_smtppassword": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpname": "***REMOVED SENSITIVE VALUE***",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpauth": true,
        "mail_smtpport": "587",
        "overwriteproto": "https",
        "trusted_proxies": "***REMOVED SENSITIVE VALUE***",
        "default_phone_region": "DE",
        "maintenance_window_start": 2,
        "dav.defaults.webcal.refresh": 86400,
        "config_preset": 0,
        "app_install_overwrite": [],
        "loglevel": 2
    }
}

Web server error log

No related entries.

Log file

No log entries related to the manual .ics import — the failure is completely silent.

Browser log

Additional info

No response

The issue names no source files, tests, or entry points. Start by reproducing the subscription import with the two attached ICS files and comparing their parsing behavior; trace the calendar subscription import path from there. Done means the second valid calendar imports its events without a silent failure, with coverage for the reported format.