“Failed to save event” when adding new attendee to a recurring event

Steps to reproduce

1. Create a new recurring event (e.g., weekly or daily).
2. Save it successfully.
3. Reopen the event and add a new participant (attendee).
4. Try to save the event.

Expected behavior

The recurring event should update successfully and include the newly added participant(s).

Actual behavior

The system displays an error:

“Failed to save event”

and the change is not applied.

Calendar app version

5.3.7

CalDAV-clients used

no

Browser

Firefox 130

Client operating system

Windows 10

Server operating system

Linux 6.1.0-35-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.137-1 (2025-05-07) x86_64

Web server

None

Database engine version

MySQL

PHP engine version

PHP 8.3

Nextcloud version

30.0.13 - 30.0.13.1

Updated from an older installed version or fresh install

None

List of activated apps

Nextcloud configuration

Web server error log

Log file

Browser log

Additional info

This issue affects all users in our organization who manage recurring meetings.
Currently, the only workaround is to delete the recurring event and recreate it whenever the attendee list changes.
This is time-consuming, especially when many participants are involved.

Could you please confirm whether this issue is already known, and if a fix or workaround is planned for an upcoming release?