Confusion about ACL Files in Shared Mailboxes

Hello, I have a shared mailbox which I want to set ACL permissions to. I already tried "doveadm acl set -u shared-user Shared/shared_mailbox group=somegroup lookup read write write-seen write-deleted insert post delete expunge create" My shared namespace is configured like this: "type = shared, prefix = Shared/%%u" I get "Error: Can't update acl object '': No local acl file path", "Error: Mailbox Shared/shared_mailbox: Failed to set ACL". When I do "* group=some_group kxeilprwts" in dovecot-acl in the shared Mailbox, all users in group some_group lose all access to their folders (shared and not shared) except INBOX. What am I doing wrong?