Due date of repeating tasks not updated in NC Tasks GUI after completion in Thunderbird

[topas-rec]

( Ok, I read this and my issue is close, but I think the server core works in this case)

Steps to reproduce

1. Complete a previously (perfectly ;-)) synced repeating task in Thunderbird (Task was due in the past and next due date in Thunderbird is also in the past - not very important I think but now it is made clear)
2. Sync it (Press synchronize in Thunderbird)
3. Compare the due date of the task in nextcloud tasks with the due date of Thunderbird and see the nextcloud due date hasn't changed.

( Lets check if the sync itself worked as guessed by Thunderbird dev team:https://bugzilla.mozilla.org/show_bug.cgi?id=1534105)

4. Export the calendar of the Task to an ics file in nextcloud
5. Import the ics file into a calendar in a local (not network) calendar inThunderbird
6. Compare the due dates of the network calendar with the recently imported task (They are the same - That means nextcloud has received the change, but the Tasks app does not show them - I guess)

Expected behaviour

The due date update after the sync is shown in the UI

Actual behaviour

Due date stays on previous value

Server configuration

Operating system: Linux Mint 18

Web server: apache (Nextcloud docker image 15.0.4)

Database: mariadb

PHP version: 7.2.15

Nextcloud version: 15.0.4

Tasks version: 0.9.8

Updated from an older Nextcloud or fresh install: (Updated, new docker container, data then upgrades as described in https://github.com/nextcloud/docker/tree/master/.examples section)

Signing status: ?

Login as admin user into your Nextcloud and access 
http://example.com/index.php/settings/integrity/failed 
paste the results here.


Example Domain

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More information...

(My server runs in a local network only)

List of activated apps:

If you have access to your command line run e.g.:
sudo -u www-data php occ app:list
from within your Nextcloud installation folder

Enabled:
  - accessibility: 1.1.0
  - activity: 2.8.2
  - bookmarks: 0.16.2
  - calendar: 1.6.4
  - cloud_federation_api: 0.1.0
  - comments: 1.5.0
  - contacts: 3.0.3
  - dav: 1.8.1
  - federatedfilesharing: 1.5.0
  - federation: 1.5.0
  - files: 1.10.0
  - files_external: 1.6.0
  - files_pdfviewer: 1.4.0
  - files_sharing: 1.7.0
  - files_texteditor: 2.7.0
  - files_trashbin: 1.5.0
  - files_versions: 1.8.0
  - files_videoplayer: 1.4.0
  - firstrunwizard: 2.4.0
  - gallery: 18.2.0
  - logreader: 2.0.0
  - lookup_server_connector: 1.3.0
  - nextcloud_announcements: 1.4.0
  - notifications: 2.3.0
  - oauth2: 1.3.0
  - password_policy: 1.5.0
  - provisioning_api: 1.5.0
  - serverinfo: 1.5.0
  - sharebymail: 1.5.0
  - support: 1.0.0
  - survey_client: 1.3.0
  - systemtags: 1.5.0
  - tasks: 0.9.8
  - theming: 1.6.0
  - twofactor_backupcodes: 1.4.1
  - updatenotification: 1.5.0
  - workflowengine: 1.5.0
Disabled:
  - admin_audit
  - encryption
  - user_ldap

Nextcloud configuration:

If you have access to your command line run e.g.:
sudo -u www-data php occ config:list system
from within your instance's installation folder

{
    "system": {
        "htaccess.RewriteBase": "\/",
        "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
            }
        ],
        "instanceid": "***REMOVED SENSITIVE VALUE***",
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "192.168.178.24"
        ],
        "datadirectory": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "15.0.4.0",
        "overwrite.cli.url": "http:\/\/192.168.178.24",
        "dbname": "***REMOVED SENSITIVE VALUE***",
        "dbhost": "***REMOVED SENSITIVE VALUE***",
        "dbport": "",
        "dbtableprefix": "",
        "mysql.utf8mb4": true,
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "maintenance": false,
        "loglevel": 2
    }
}

or

Insert your config.php content here
Make sure to remove all sensitive content such as passwords. (e.g. database password, passwordsalt, secret, smtp password, …)

Are you using external storage, if yes which one: External storage NTFS

Are you using encryption: no

Are you using an external user-backend, if yes which one: No

Client configuration

Browser: Firefox

Operating system: Linux Mint 18

CalDAV-clients: Thunderbird 60.5.1, Lightning 6.2.5

Logs

Web server error log

Insert your webserver log here

Nextcloud log (data/nextcloud.log)

Insert your Nextcloud log here

Checked the logs. No entries when this issue comes up.

Browser log

Insert your browser log here, this could for example include:

a) The javascript console log
b) The network log 
c) ...