@dc42 , @bearer Here was my mistake:
To configure the magnetometer, I sent
M260 A"0x0C" B"0x60:0x00:0x5C:00" R1
which is nonsense to the firmware.
I stopped using the array of hex values and instead (correctly) used an array of decimal values :
M260 A12 B96:0:92:0 R1
Things started working. Thank you, both.