Internal server error when querying boards

I’m running the following query:

query QuerySharedBoards ($limit: Int, $page: Int) {
	boards (limit: $limit, page: $page, board_kind: share) {
		id
		board_folder_id
		board_kind
		creator {
			account {
				slug
			}
			id
		}
		description
		# items_count - complexity too high - see package documenatation above
		name
		permissions
		owners {
			id
			email
			name
		}
		state
		subscribers {
			id
			email
			name
			is_guest
		}
		type
		updated_at
		workspace_id
	}
}

and getting an internal server error (500 status code)

When removing the is_guest and email from the subscribers, everything works perfect.
My question is why? When I look for subscribers at the schema I do see that those should be a list of User which do have those properties.

Thanks!