Error: rmdir messages are permanently generated in the log

I have this error message in the Nextcloud Log every view seconds, but the system is working. what happens there exactly?

[PHP] Error: Error: rmdir(/tmp//oc_tmp_M9i2dm-folder) [<a href='https://secure.php.net/manual/en/function.rmdir.php'>function.rmdir.php</a>]: Operation not permitted at /xxxxx/xxxxxx/www/xxx.xxxxx.xx/lib/private/legacy/OC_Helper.php#178 at <<closure>>

0. <<closure>>
   OC\Log\ErrorHandler::onError(2, "rmdir(/tmp//oc_ ... d", "/home/xxxxxxxx/ ... p", 178, {dir: "/tmp//oc_ ... }})
1. /xxxxx/xxxxxxxx/www/xxxxx.xxxxx.xx/lib/private/legacy/OC_Helper.php line 178
   rmdir("/tmp//oc_tmp_M9i2dm-folder")
2. /xxxxx/xxxxxxx/xxx/xxxxx.xxxxx.xx/lib/private/TempManager.php line 163
   OC_Helper::rmdirr("/tmp//oc_tmp_M9i2dm-folder")
3. /xxxxx/xxxxxx/xxxx/xxx.xxxxx.xx/lib/private/TempManager.php line 181
   OC\TempManager->cleanFiles(["/tmp//oc_tmp_U ... "])
4. /xxxxx/xxxxxx/xxxxx/xxx.xxxxxx.xx/cron.php line 72
   OC\TempManager->cleanOld()

GET /cron.php
from 188.154.245.21 at 2021-02-05T18:57:58+00:00

Steps to reproduce

If I knew, I would tell you.

Expected behaviour

In and of itself, the Nextcloud installation runs, but it cannot be the goal that these error messages are permanently generated.

Actual behaviour

Since 10days, the update to version 20.0.5, these error messages are generated permanently.

Server configuration detail

Operating system: FreeBSD 11.4-RELEASE-p2 FreeBSD 11.4-RELEASE-p2 #2 r363941M: Thu Aug 6 06:58:24 UTC 2020 root@fbsd-build01.adm.hostpoint.ch:/usr/obj/usr/src/sys/HOSTPOINT amd64

Webserver: Apache (cgi-fcgi)

Database: mysql 10.3.27

PHP version:

7.4.14
Modules loaded: Core, date, libxml, pcre, hash, Reflection, SPL, session, standard, cgi-fcgi, mysqlnd, apcu, bcmath, bz2, calendar, ctype, curl, dba, dom, mbstring, fileinfo, filter, ftp, gd, gettext, gmp, gnupg, iconv, imagick, intl, jsmin, json, ldap, exif, mcrypt, mysqli, odbc, openssl, pcntl, PDO, pgsql, zlib, posix, pspell, readline, SimpleXML, snmp, soap, sockets, sodium, sqlite3, ssh2, sysvmsg, sysvsem, sysvshm, tidy, tokenizer, xml, xmlwriter, yaml, zip, Phar, imap, mailparse, mongodb, PDFlib, pdo_dblib, pdo_mysql, pdo_pgsql, pdo_sqlite, scrypt, xmlreader, xmlrpc, xsl, Zend OPcache

Nextcloud version: 20.0.5 - 20.0.5.2

Updated from an older Nextcloud/ownCloud or fresh install: 20.0.5

Where did you install Nextcloud from: unknown

Signing status

Array
(
)

List of activated apps
Enabled:
 - accessibility: 1.6.0
 - activity: 2.13.4
 - bruteforcesettings: 2.0.1
 - calendar: 2.1.3
 - cloud_federation_api: 1.3.0
 - comments: 1.10.0
 - contacts: 3.4.3
 - contactsinteraction: 1.1.0
 - dashboard: 7.0.0
 - dav: 1.16.2
 - federatedfilesharing: 1.10.2
 - federation: 1.10.1
 - files: 1.15.0
 - files_pdfviewer: 2.0.1
 - files_rightclick: 0.17.0
 - files_sharing: 1.12.2
 - files_trashbin: 1.10.1
 - files_versions: 1.13.0
 - files_videoplayer: 1.9.0
 - firstrunwizard: 2.9.0
 - issuetemplate: 0.7.0
 - logreader: 2.5.0
 - lookup_server_connector: 1.8.0
 - nextcloud_announcements: 1.9.0
 - notifications: 2.8.0
 - oauth2: 1.8.0
 - password_policy: 1.10.1
 - photos: 1.2.3
 - privacy: 1.4.0
 - provisioning_api: 1.10.0
 - recommendations: 0.8.0
 - richdocuments: 3.7.11
 - serverinfo: 1.10.0
 - settings: 1.2.0
 - sharebymail: 1.10.0
 - spreed: 10.0.5
 - support: 1.3.0
 - survey_client: 1.8.0
 - systemtags: 1.10.0
 - text: 3.1.0
 - theming: 1.11.0
 - twofactor_backupcodes: 1.9.0
 - updatenotification: 1.10.0
 - user_status: 1.0.1
 - viewer: 1.4.0
 - weather_status: 1.0.0
 - workflowengine: 2.2.0
Disabled:
 - admin_audit
 - encryption
 - files_external
 - mail
 - user_ldap

Configuration (config/config.php)
{
    "instanceid": "***REMOVED SENSITIVE VALUE***",
    "passwordsalt": "***REMOVED SENSITIVE VALUE***",
    "secret": "***REMOVED SENSITIVE VALUE***",
    "trusted_domains": [
        "cloud.kings.mw"
    ],
    "datadirectory": "***REMOVED SENSITIVE VALUE***",
    "dbtype": "mysql",
    "version": "20.0.5.2",
    "overwrite.cli.url": "https:\/\/cloud.kings.mw",
    "dbname": "***REMOVED SENSITIVE VALUE***",
    "dbhost": "***REMOVED SENSITIVE VALUE***",
    "dbport": "",
    "dbtableprefix": "oc_",
    "mysql.utf8mb4": true,
    "dbuser": "***REMOVED SENSITIVE VALUE***",
    "dbpassword": "***REMOVED SENSITIVE VALUE***",
    "installed": true
}

Are you using external storage, if yes which one: local/smb/sftp/…

Are you using encryption:

Are you using an external user-backend, if yes which one: LDAP/ActiveDirectory/Webdav/…

Client configuration

Browser: Chromium 88.0.4324.96

Operating system: Ubuntu 20.04

Logs

Web server error log
Insert your web server log here 
Nextcloud log
[PHP] Error: Error: rmdir(/tmp//oc_tmp_M9i2dm-folder) [<a href='https://secure.php.net/manual/en/function.rmdir.php'>function.rmdir.php</a>]: Operation not permitted at /xxxxx/xxxxxx/www/xxx.xxxxx.xx/lib/private/legacy/OC_Helper.php#178 at <<closure>>

0. <<closure>>
   OC\Log\ErrorHandler::onError(2, "rmdir(/tmp//oc_ ... d", "/home/xxxxxxxx/ ... p", 178, {dir: "/tmp//oc_ ... }})
1. /xxxxx/xxxxxxxx/www/xxxxx.xxxxx.xx/lib/private/legacy/OC_Helper.php line 178
   rmdir("/tmp//oc_tmp_M9i2dm-folder")
2. /xxxxx/xxxxxxx/xxx/xxxxx.xxxxx.xx/lib/private/TempManager.php line 163
   OC_Helper::rmdirr("/tmp//oc_tmp_M9i2dm-folder")
3. /xxxxx/xxxxxx/xxxx/xxx.xxxxx.xx/lib/private/TempManager.php line 181
   OC\TempManager->cleanFiles(["/tmp//oc_tmp_U ... "])
4. /xxxxx/xxxxxx/xxxxx/xxx.xxxxxx.xx/cron.php line 72
   OC\TempManager->cleanOld()

GET /cron.php
from 188.154.245.21 at 2021-02-05T18:57:58+00:00