⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• Nextcloud Server is running on 64bit capable CPU, PHP and OS.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

The reminder notifications and invitations behaviour is unpredictable and pretty random. Something is definitely broken.
I could reproduce this issue in Nextcloud 25 RC2 and various older production Nextcloud 24's

Two scenarios:

Send reminder notifications to calendar sharees as well set to off:

What should happen with a private calender:

The organizer creates a calendar entry and invites one person.

• Organizer and invitee get an invitation
• Organizer and invitee get a reminder notification (Error: here in the setup both always get two reminders, so one too many)

What should happen with a group calender:

The organizer creates a calendar entry and invites one person.

• Organizer gets an invitation
• Invitee doesn't get an invitation. (Error: The invitee does not receive an invitation!)
• Organizer and invitee get a reminder (Error: The reminder is not sent e.g. 5 minutes before but only at the time of the appointment)

Send reminder notifications to calendar sharees as well set to on:

Then everyone in the group will receive a notification even though they are not included in the appointment as a participant. That's how it's intended. (So the principle is correct. So only the invitation is missing here.)

So the boil down the issues:

1. Private calender, off -> double notifications
2. Group calendar -> Invitees doesn't get invitation (Invitees should always get an invitation)
3. Group calendar, off -> reminder notifications are sent only at exact appointment time

Probably related:

• Calendar sends duplicate notifications if there is an additional attendee [$250] #21370
• event reminder is missing in a shared calendar w/o edit rights #22441
• Rename setting 'sendEventRemindersToSharedGroupMembers' -> 'sendEventRemindersToSharedUsers'. #31660
• Fix #31303: Make reminder notification behaviour selectable.. #31337

Thanks to @mircokam for spotting this issues.

Steps to reproduce

1. Create a group calendar
2. Add member to group calendar
3. Create an event in said group calendar
4. Add an e-mail address to invitees
5. Add an Nextcloud user to invitees
6. Add event reminder notification e.g. 5 minutes before event

Expected behavior

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Installation method

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Operating system

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PHP engine version

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Web server

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Database engine version

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Is this bug present after an update or on a fresh install?

Fresh Nextcloud Server install

Are you using the Nextcloud Server Encryption module?

No response

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

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List of activated Apps

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Nextcloud Signing status

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Nextcloud Logs

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Additional info

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