Console V3 has the ability to download a global_conf.json. Compare the GatewayID from the console with GatewayID from the global_conf.json and you can see that this can lead to confusion.
GatewayID in global_conf.json is GatewayEUI in console?
You are correct, what appears on the console as EUI is referred to as ID in that file.
Just makes for a little wrinkle to trip us up with!
… and it appears that this was the reason for the error ERROR: [main] failed to start the concentrator.
I modified the GatewayID in global_conf.json and the gateway is now online in V3