Shares to external storage gone after migration

Nextcloud version: 21

We recently migrated a nextcloud with an external SMB storage attached. after the migration the servername to the external storage was changed but nothing else. after doing this, the checkmark went green and everything seemed to be fine. (authentication was “global authentication”, so, just a usernme/password), the admin user could browse the external storage.

but… we share subfolders from the external storage to other nextcloud users and these shares are all gone. we see the shares in the db, the user sees the folders, but they are empty. when we add the shares manually again, we get a new folder “share name (1)” within the users account and he can browse the files again.

what can we do here to migrate the old shares to the new external storage?