Migrating validators from one node to another (or from one vm instance to another) requires careful attention to avoid slashing. If you accidentally run the same validator key on 2 instances at the same time, even for a very short time period, you risk being slashed for an Attestation Violation. If this occurs, you will be removed as a validator and your GNO will be frozen and unavailable for withdrawal until after the GC/GBC merge.