Part of a structured data set won't transmit between 2 RFM69

[J-M-L]

Did you try to print what you receive?

for (byte i = 0; i < radio.DATALEN; i++) {
  Serial.print((byte)radio.DATA[i], HEX);
  Serial.write(' ');
}

May be on the sender side put easily recognizable values in the struct members

And check if radio.DATALEN is the same as the struct size