Not all calendars in the "People's calendars" group are included in the list

When I try to get the list of all callendars in the "People's calendar" group some calendars are not included.
The API call:
me/calendarGroups/{calendargroup Id of peoples-calendar-group}/calendars

Calendars which are added by the following steps are not included, but are shown in the OWA client:
- Goto https://outlook.office.com/calendar/view/week

- Click "Add calendar"

- Click "Add from directory"

- Select your account

- Select a person who's calendar you want to add (in my case "John Doe")

In outllook it will show you the "John Doe" calendar, but when getting the list via the graph API all other calendars are returned, except for John Doe.

How can I retrieve the full list?