Background - within NVMC-nms2-db _owner fields reflect which service_manager.smgr_id the device/instance record came from, vs _mapping fields which reflect the local_id within that poller's nms2-db. So then within NV_P0n-nms2-db both _owner & _mapping fields are unused.
In this case a couple of devices within the MC-nms2 space had valid _owner values, but somehow ended up with _mapping=0 record values. Not valid. Presumably this could come from an unplanned topology-restart while the device/instance was just getting inserted into the nvmc-db.