Mails datetime is based on the file last change time instead of arrive date

I setup a new server and pasted a backup of my nextcloud and mailserver.
Anything works fine but the time shows always "7 days before" (just in a other language).
Thunderbird, Roundcube and my mobile Phone shows the correct arrive date!

Expected behavior

Show the correct datetime when the mail arrived.

Actual behavior

Shows the last change time from the mail file!

Mail app

Mail app version: (see apps admin page, e.g. 0.5.3)
0.8.1
Mailserver or service: (e.g. Outlook, Yahoo, Gmail, Exchange,...)
own
Number of accounts: (e.g. 1 or 2)
1

Server configuration

Operating system: (e.g. Debian 8)
Debian 8
Web server: (e.g. Apache, Nginx,...)
Apache
Database: (e.g. MariaDB, SQLite, PostgreSQL,...)
MariaDB
PHP version: (e.g. 7.0)
7.1

Nextcloud Version: (see admin page, e.g. 13.0.2)
13.0.2
Updated from an older version or fresh install:
fresh install
List of activated apps:

Enabled:                                                                                                                                                                                                            
  - activity: 2.6.1                                                                                                                                                                                                 
  - calendar: 1.6.1                                                                                                                                                                                                 
  - caniupdate: 0.1.2                                                                                                                                                                                               
  - comments: 1.3.0                                                                                                                                                                                                 
  - contacts: 2.1.3                                                                                                                                                                                                 
  - dav: 1.4.6
  - deck: 0.3.1
  - federatedfilesharing: 1.3.1
  - federation: 1.3.0
  - files: 1.8.0
  - files_pdfviewer: 1.2.1
  - files_rightclick: 0.8.4
  - files_sharing: 1.5.0
  - files_texteditor: 2.5.1
  - files_trashbin: 1.3.0
  - files_versions: 1.6.0
  - files_videoplayer: 1.2.0
  - firstrunwizard: 2.2.1
  - gallery: 18.0.0
  - issuetemplate: 0.3.0
  - logreader: 2.0.0
  - lookup_server_connector: 1.1.0
  - mail: 0.8.1
  - nextcloud_announcements: 1.2.0
  - notifications: 2.1.2
  - oauth2: 1.1.0
  - onlyoffice: 1.3.0
  - password_policy: 1.3.0
  - provisioning_api: 1.3.0
  - serverinfo: 1.3.0
  - sharebymail: 1.3.0
  - survey_client: 1.1.0
  - systemtags: 1.3.0
  - theming: 1.4.1
  - twofactor_backupcodes: 1.2.3
  - updatenotification: 1.3.0
  - workflowengine: 1.3.0
Disabled:
  - admin_audit
  - encryption
  - files_external
  - user_external
  - user_ldap

The content of config/config.php:

{
    "system": {
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "***REMOVED SENSITIVE VALUE***"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "overwrite.cli.url": "https:\/\/***REMOVED SENSITIVE VALUE***\/nextcloud",
        "dbtype": "mysql",
        "version": "13.0.2.1",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpmode": "php",
        "mail_smtpauthtype": "LOGIN",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "loglevel": 0,
        "maintenance": false,
        "theme": ""
    }
}

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Reproduce the issue by restoring the reported mail backup and compare the displayed relative time with the arrival date shown by Thunderbird, Roundcube, and the mobile client. Trace how the Mail app derives message datetime from the mail file and verify that the displayed value uses the arrival date rather than the file's last-change time.