Events with RRULE get imported into the incorrect day with different timezones (enough for the day to differ from the inviter's TZ)

[shtrom]

Steps to reproduce

Maybe a similar issue to #6407, but in a different context: receiving an invitation with an RRULE from GCalendar in UTC-0400 when my Nextloud instance is in UTC+1000. When importing the ICS into Nexctloud, and getting it back out with vdirsyncer, I can see that the timezone in the ICS file has been updated to my local TZ, but the RRULE hasn't been updated accordingly, even if the event would be the next day for me.

1. GCalendar in UTC-0600: invite a Nextcloud user late in the day (e.g., 16:00), with a weekly reccurence
2. Import invite into Nextcloud
3. Observe events in Nextcloud are at the right time, but a day early.

Expected behavior

Recurring events created, and shown at the correct (TZ-adjusted) time and days of the week.

Actual behaviour

Recurring events created, and shown at the correct (TZ-adjusted) time, BUT the days of the week are those in the original timezone (i.e., day before).

Calendar app version

No response

CalDAV-clients used

DAVx5, vdirsyncer

Browser

Firefox 132

Client operating system

Arch

Server operating system

Debian, official Docker container

Web server

Nginx

Database engine version

MariaDB

PHP engine version

PHP 8.2

Nextcloud version

29.0.8

Updated from an older installed version or fresh install

None

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

Observation in the ICS:

• The original invitation attached to the email from GCal is in the sender's timezone:

DTSTART;TZID=America/Toronto:20241003T163000
DTEND;TZID=America/Toronto:20241003T173000
RRULE:FREQ=WEEKLY;WKST=SU;BYDAY=WE,MO,TH

• The event created in Nextcloud has been converted to the local timezone (and the next day), BUT the RRULE hasn't been updated:

DTSTART;TZID=Australia/Sydney:20241004T063000
DTEND;TZID=Australia/Sydney:20241004T073000
RRULE:FREQ=WEEKLY;WKST=SU;UNTIL=20241028T035959Z;BYDAY=WE,MO,TH

• The updated RRULE should contain BYDAY=TH,TU,FR

[SebastianKrupinski]

Hi @shtrom

The time zone should not be changed when importing the event, can you maybe post the original calendar invitation from GCalendar (you can redact all personal information)? There is a time zone block that I need to see.

Also, how was the event imported, through the mail app?

Sebastian