[GH-ISSUE #399] caldavsynchronizer deletes periodically a bunch of calender entries #382

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opened 2026-02-25 20:31:32 +03:00 by kerem · 4 comments

kerem commented

2026-02-25 20:31:32 +03:00

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Originally created by @Beleggrodion on GitHub (Jul 12, 2023).
Original GitHub issue: https://github.com/aluxnimm/outlookcaldavsynchronizer/issues/399

Windows Version: Windows 11 (10.0.22621.0)
Outlook Version: Outlook Office 365 (detailed version pending, i asked the user)
CalDavSynchronizer Version: 4.4.1.0
CalDav/Cardav Server Version: Nextcloud 26.0.3 (Calendar App 4.4.3)

I had a strange issue on one of the users on my nextcloud instance which uses outlookcaldavsynchonizer to sync his calendar (and that from his collegues in the non-profit association) that only many of his calendar items get deleted. When the delete process occures looks like random. First occured at the beginning of june 2-3 times then was now all good until last week friday when it happens again and now yesterday.

The logfile on the nextcloud don't say much for it, it say's all looks i.o. Also the Debug Log don't tell me much. So i think also for caldavsynchonizer it looks all ok,. It only sa's that Btype delta deleted 19 entries and the followd list of DEBUG messages with ItemAction.Delete are the missing appointments which he then missed.

Currently i always send him the backup of the calendar of the last night, so that he can reimport the calendar items at once and don't need to click on each appointment in the nextcloud recycle bin to restore it. But this cannot be the permanent solution.

So the question is, has someone else also that problem? and when yes, was there a solution?
Or is their the possible to save the ics files (for debugging) which caldavsynchronizer downloads to process so that looking into it is possible to check if nextcloud generate's here wrong ics files (ex. missing appointments) or of they look ok and caldavsynchonizer interpretes them wrong?

Originally created by @Beleggrodion on GitHub (Jul 12, 2023). Original GitHub issue: https://github.com/aluxnimm/outlookcaldavsynchronizer/issues/399 Windows Version: Windows 11 (10.0.22621.0) Outlook Version: Outlook Office 365 (detailed version pending, i asked the user) CalDavSynchronizer Version: 4.4.1.0 CalDav/Cardav Server Version: Nextcloud 26.0.3 (Calendar App 4.4.3) I had a strange issue on one of the users on my nextcloud instance which uses outlookcaldavsynchonizer to sync his calendar (and that from his collegues in the non-profit association) that only many of his calendar items get deleted. When the delete process occures looks like random. First occured at the beginning of june 2-3 times then was now all good until last week friday when it happens again and now yesterday. The logfile on the nextcloud don't say much for it, it say's all looks i.o. Also the Debug Log don't tell me much. So i think also for caldavsynchonizer it looks all ok,. It only sa's that Btype delta deleted 19 entries and the followd list of DEBUG messages with ItemAction.Delete are the missing appointments which he then missed. Currently i always send him the backup of the calendar of the last night, so that he can reimport the calendar items at once and don't need to click on each appointment in the nextcloud recycle bin to restore it. But this cannot be the permanent solution. So the question is, has someone else also that problem? and when yes, was there a solution? Or is their the possible to save the ics files (for debugging) which caldavsynchronizer downloads to process so that looking into it is possible to check if nextcloud generate's here wrong ics files (ex. missing appointments) or of they look ok and caldavsynchonizer interpretes them wrong?

kerem commented

2026-02-25 20:31:32 +03:00

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@brrrrrrrt commented on GitHub (Aug 8, 2023):

+1 experiencing the same thing for a long time, not sure but so far it only happened on users using more than one device.

@brrrrrrrt commented on GitHub (Aug 8, 2023): +1 experiencing the same thing for a long time, not sure but so far it only happened on users using more than one device.

kerem commented

2026-02-25 20:31:32 +03:00

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@kdoteu commented on GitHub (Nov 3, 2023):

I got a similar problem. I synced a new User with his already existing Outlook calender towards Nextcloud everything works fine. I changed the sync to "Two-Way" and every Entry got deleted. For other users everything works fine.

I noticed some special things, eventually this is "problem".
The calendar which is going to be synced is an Exchange-calendar (got synced with online outlook.com). When I restore some entrys and force a sync in outlook, I can see the entries for a second or so. After this they disappear and got deleted.

Hope eventually somebody can tackle this problem down. If some more information are needed, pls post i going to provide details as possible.

@kdoteu commented on GitHub (Nov 3, 2023): I got a similar problem. I synced a new User with his already existing Outlook calender towards Nextcloud everything works fine. I changed the sync to "Two-Way" and every Entry got deleted. For other users everything works fine. I noticed some special things, eventually this is "problem". The calendar which is going to be synced is an Exchange-calendar (got synced with online outlook.com). When I restore some entrys and force a sync in outlook, I can see the entries for a second or so. After this they disappear and got deleted. Hope eventually somebody can tackle this problem down. If some more information are needed, pls post i going to provide details as possible.

kerem commented

2026-02-25 20:31:32 +03:00

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@Beleggrodion commented on GitHub (Jun 25, 2024):

It looks like no one of the dev's is intrested to fix this problem. no reaction, not even a request for more information. I also added on sourceforge for another problem some comments to the tickets of other people, also with no reactions. I normaly don't bump tickets, but because the non-profit association is a little bit pissed and i'm too.

@Beleggrodion commented on GitHub (Jun 25, 2024): It looks like no one of the dev's is intrested to fix this problem. no reaction, not even a request for more information. I also added on sourceforge for another problem some comments to the tickets of other people, also with no reactions. I normaly don't bump tickets, but because the non-profit association is a little bit pissed and i'm too.

kerem commented

2026-02-25 20:31:32 +03:00

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@mmmagk commented on GitHub (Oct 14, 2025):

I have the same issue with version 4.6.0 of CalDavSynchronizer and Outlook 2016. It seems that if Outlook crashes it (or CalDavSyncronizer) starts a batch deletion of calendar entries. It seems to be starting with the oldest ones and in my case I received hundreds of mails with meeting cancellations and lots of Mail Delivery Error Mails because a lot of the participant's mail addresses were no longer valid (e.g. they changed jobs to a new company).

It would really be great to add some kind of safe guard that avoid the deletion of 10+ or 50+ calendar entries in just a few seconds, where the system asks for confirmation or something.

@mmmagk commented on GitHub (Oct 14, 2025): I have the same issue with version 4.6.0 of CalDavSynchronizer and Outlook 2016. It seems that if Outlook crashes it (or CalDavSyncronizer) starts a batch deletion of calendar entries. It seems to be starting with the oldest ones and in my case I received hundreds of mails with meeting cancellations and lots of Mail Delivery Error Mails because a lot of the participant's mail addresses were no longer valid (e.g. they changed jobs to a new company). It would really be great to add some kind of safe guard that avoid the deletion of 10+ or 50+ calendar entries in just a few seconds, where the system asks for confirmation or something.