[GH-ISSUE #405] Some Calendar entries deleted, others duplicated in each sync process on all devices #857

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opened 2026-03-01 17:41:57 +03:00 by kerem · 4 comments

kerem commented

2026-03-01 17:41:57 +03:00

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Originally created by @ImNotAProgramer on GitHub (Oct 16, 2023).
Original GitHub issue: https://github.com/aluxnimm/outlookcaldavsynchronizer/issues/405

Versions as of 16.10.2023:
CalDavSynchronizer Version: 4.4.1.0
Windows 11 Home, 22H2, build 22621.2428
Outlook: Microsoft 365 MSO (Version 2309 Build 16.0.16827.20166) 64 Bit

Syncing a Google calendar between PC Outlook and two Android "Google Workspace Calendar"

Is this only me, or does anyone else have this issue? All entries are being duplicated each sync. A lot of new entries are missing.
This just started to happen/ I just noticed it.

I am definitely missing a calendar entry on the 23.10. And there are more.

Example Screenshot:

Originally created by @ImNotAProgramer on GitHub (Oct 16, 2023). Original GitHub issue: https://github.com/aluxnimm/outlookcaldavsynchronizer/issues/405 Versions as of 16.10.2023: CalDavSynchronizer Version: 4.4.1.0 Windows 11 Home, 22H2, build 22621.2428 Outlook: Microsoft 365 MSO (Version 2309 Build 16.0.16827.20166) 64 Bit Syncing a Google calendar between PC Outlook and two Android "Google Workspace Calendar" Is this only me, or does anyone else have this issue? All entries are being duplicated each sync. A lot of new entries are missing. This just started to happen/ I just noticed it. I am definitely missing a calendar entry on the 23.10. And there are more. Example Screenshot: ![CalDAV Calendar issue](https://github.com/aluxnimm/outlookcaldavsynchronizer/assets/19426964/e699bbc4-e950-4ac1-b72e-df291439f888)

kerem commented

2026-03-01 17:41:58 +03:00

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@fitus85 commented on GitHub (Dec 7, 2023):

I have the same problems with:
CalDavSynchronizer Version: 4.4.1.0
2x Outlook on Office Desk PC and on Homeoffice Notebook: Microsoft 365 MSO (Version 2310 Build 16.0.16924.20054) 32 Bit
Outlook is connected to Kopano via Z-Push
CalDav Server to sync with is Nextcloud 27.1.4

I could not find any rule on which items getting doubled or more.
Definitely will items get deleted randomly.

@fitus85 commented on GitHub (Dec 7, 2023): I have the same problems with: CalDavSynchronizer Version: 4.4.1.0 2x Outlook on Office Desk PC and on Homeoffice Notebook: Microsoft 365 MSO (Version 2310 Build 16.0.16924.20054) 32 Bit Outlook is connected to Kopano via Z-Push CalDav Server to sync with is Nextcloud 27.1.4 I could not find any rule on which items getting doubled or more. Definitely will items get deleted randomly.

kerem commented

2026-03-01 17:41:58 +03:00

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@rmeissn commented on GitHub (May 15, 2024):

My friend also tried to sync Outlook with a shared google calender and ended up having thousands of duplicated entries in her calendar with no visible reason or switch for it.
She used v4.4.1.0

@rmeissn commented on GitHub (May 15, 2024): My friend also tried to sync Outlook with a shared google calender and ended up having thousands of duplicated entries in her calendar with no visible reason or switch for it. She used v4.4.1.0

kerem commented

2026-03-01 17:41:58 +03:00

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@rmeissn commented on GitHub (May 16, 2024):

Just for anyone in need of it:
I've created two python scripts, based on https://github.com/VladislavEkimtcov/PythonICSDuplicateRemover/tree/master

The first processes an exported ICS file through a calendar library and removes every event after a specific date (duplicated events got this "after date XYZ"). The second one processes the input ICS line by line and also removes everything after a specific date. The latter script might be better in terms of events it can handle, as the calendar library got some drawbacks.

Just edit the files (regarding input filename & date after which events are deleted) and execute these with python <program>.py to produce a ICS file with deduplicated events.

ICS duplicate remover.zip

@rmeissn commented on GitHub (May 16, 2024): Just for anyone in need of it: I've created two python scripts, based on https://github.com/VladislavEkimtcov/PythonICSDuplicateRemover/tree/master The first processes an exported ICS file through a calendar library and removes every event after a specific date (duplicated events got this "after date XYZ"). The second one processes the input ICS line by line and also removes everything after a specific date. The latter script might be better in terms of events it can handle, as the calendar library got some drawbacks. Just edit the files (regarding input filename & date after which events are deleted) and execute these with `python <program>.py` to produce a ICS file with deduplicated events. [ICS duplicate remover.zip](https://github.com/aluxnimm/outlookcaldavsynchronizer/files/15330839/ICS.duplicate.remover.zip)

kerem commented

2026-03-01 17:41:58 +03:00

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@Mannshoch commented on GitHub (Nov 6, 2025):

Same Problem here. I have setup as replicate but even then Caldavsyncadater does not remove duplicated entries.

source: outlook 365, caldavsyncadapter 4.6.0
destination: Nextcloud 31.0.8, calender oneway replicated. ( for sharing )

@Mannshoch commented on GitHub (Nov 6, 2025): Same Problem here. I have setup as replicate but even then Caldavsyncadater does not remove duplicated entries. - source: outlook 365, caldavsyncadapter 4.6.0 - destination: Nextcloud 31.0.8, calender oneway replicated. ( for sharing )