All measurements are hidden when a gateway is moved to a new location (excluding GPS drift within a 100m area).
When configuring your gateway’s location, please follow this logic flow to prevent confusion where the location information comes from:
Gateways are only shown on TTN Mapper by default if there are measured points for it. So you are right to see it hidden after the move.
Do not delete and re-add your gateway on the console. You will not be able to re-register a gateway with the same ID on the current version of the console.