I am quite sure that last year I connected RN2483 with MultiTech gateway and it worked without any problem but I’m unsure from which firmware version this problem has been introduced.
Another approach is to investigate this problem if you have another LoRaWAN module from ARM mBed i.e. SX1272 or similar one from Murata and try to connect it to the same Multitech gateway and check if it works. If it works then it’s compatibility problem and Microchip or MultiTech has to find a solution for it.
I don’t know why there’s no official response on this track yet !!