The RAK2287 is based on the “new” SX1302 chip. This chip is different to the previous SX1301 chip as it has its own unique ID. Depending on the Packet Forwarder being used, the gateway may have an ID based on the Raspberry Pi, the ID extracted from the SX1302 chip or the ID set in the global_conf.json file.
I would start by inspecting the global_conf.json file
This may also give some insight into what’s happening