Events with repetition can be broken. "This recurrence rule does not generate any valid instances" exception.

Steps to reproduce

1. Create event with repetition same day every week, e.g. 5 -> 12 -> 19 -> etc
2. Delete first occurrence (5) with "Delete this occurrence"
3. Move second occurrence (12), which now became first, to e.g. 13 with editing "start from" to 13 and "Update this and all future"

Expected behavior

No user actions in native WebUI should result in an exception.

Actual behaviour

WebUI hangs and in log exception "This recurrence rule does not generate any valid instances". You can't edit title or start/to dates of this second event, only delete it or move with drag and drop. Third event (19) looks not affected of this bug.
And bug #2850 still alive, if you move event like I described in #4225

Calendar app version

4.6.0

CalDAV-clients used

No response

Browser

No response

Client operating system

No response

Server operating system

Centos 8.5

Web server

Apache

Database engine version

SQlite

PHP engine version

PHP 8.1

Nextcloud version

27.1.4

Updated from an older installed version or fresh install

Updated from an older version

List of activated apps

No response

Nextcloud configuration

No response

Web server error log

No response

Log file

No response

Browser log

No response

Additional info

No response

Start by reproducing the sequence in the native WebUI: create a weekly event, delete the first occurrence, then move the new first occurrence with “Update this and all future.” Trace the recurrence-rule handling that produces “This recurrence rule does not generate any valid instances.” Done means the update completes without hanging or throwing, and the occurrence remains editable as described.