New users added to all M365 group calendar invites

Hi,

I hope this is the right place for this question.

I've recently added 2 new M365 users and added them to a group we use. This group has the calendar in which we plan assignments for everybody. Normally the new events are visible to all group members, but we only invite the persons needed. This way people see only their own assignments in their personal calendar, but can check the group calendar to see other people's assignments if needed.

But, when adding the new members, they got added to all existing events as optional. Very annoying, because their personal calendars were full of invites.

Does anybody have a solution or know what might be the problem?