Calendar app: when sharing a calendar, the "edit" checkbox keeps getting unchecked.

Hello @ all
I want to set up a team calendar.
To do this, I created a functional account and shared its calendar.
Two groups exist: “calendar_read” and “calendar_write”.
I can check the “edit” box when selecting either the “calendar_write” group or individual accounts, but the setting reverts after a short time.

The Sharing API is enabled.
There are no conflicts regarding group membership.

Any hints?

Nextcloud is hosted on a managed Hetzner server.
Version 32.0.9, Calendar 6.4.0.

Thanks in advance

Solution?
I don’t want to go that far yet, but apparently the functional account was corrupted by the experimentation.

Everything was recreated, and it’s working so far. I’m monitoring it.