Creating events in shared calender doesn't trigger email

I have created a calender which I then shared with a group (and marked it as editable).
When creating events, an email is sent to attendes ONLY if I create the event. No mail is sent when any other user in the group is creating an event.

What can bew the cause of this?

see https://github.com/nextcloud/server/issues/26668

Thanks for the info

/Martin