UPDATE column to MIN of a SELECT result set - what went wrong?
Your problem is because it thinks that own_resource_uuid in your sub-query is res.own_resource_uuid, not asset_z_hardware.own_resource_uuid. If you specify it completely, it should be unambiguous and SQL will know what you intended.

Before you introduced res there was nothing else it could be. SQL will assume you mean a column in the local sub-query if there’s one there.