Reoccurring tasks being duplicated

[meichthys]

We have an issue where reoccurring tasks are being duplicated (regardless of the map reoccurring tasks setting).

CaldavSynchronizer version: 4.1.0.0 Outlook Verson: 2019 (Desktop) CalDAV server: Nextcloud

Steps to reproduce:

1. Create reoccurring task via outlook
2. Manually sync to nextcloud
3. Mark the task as completed via Nextcloud web interface or via a different caldav client (like another outlook synced with caldavsynchronizer)
4. The task will be marked as completed in outlook, a new task will be created, and completed tasks will continue to duplicate after each sync.

Ideally we are looking for a way to have multiple users synchronize to a shared nextcloud task list. This works for normal tasks but any reoccurring tasks are duplicated/recreated indefinitely:

[meichthys]

To add to this, I wanted to mention that I also sync reoccurring tasks from iOS to Nextcloud without any issues, so I believe the Nextcloud CalDAV server is handling things correctly.

[meichthys]

To follow up on this, I believe the issue may be with the Nextcloud Tasks web client which does not support duplicate tasks. When a duplicate task is synced to the Nextcloud web client some things are going awry. Closing this here for now.

[meichthys]

Re-opening this issue after testing with other backend caldav servers. The issue exists when syncing with other backend servers, so the problem seems to lie with either Outlook itself or CalDavSynchronizer.

[meichthys]

To follow up here, there still seems to be an issue with reoccuring tasks but the issue seems to be slightly different now.

On v4.4.0.0 the repeating tasks no longer duplicate after each sync, but the Outlook task still doesn't update to show the task as being completed (even after marking it as completed on another client - and verified on the server). Instead the outlook task is updated to match the original due date of the repeated task: Originally created task:

Here's thunderbird after marking the task as complete in thunderbird:

Here's outlook after syncing the thunderbird change:

If however i mark the repeated task as completed in Outlook, then it does properly sync to the other clients. Outlook after marked as complete:

Thunderbird after syncing: and the thunderbird detail view:

[meichthys]

@aluxnimm I was hopeful that somehow https://github.com/aluxnimm/outlookcaldavsynchronizer/issues/388 would have fixed this, but recurring tasks between multiple outlook clients is still broken in v4.4.1

[meichthys]

Closing in favor of a simpler issue report (#395).