SG= stallguard. See page 10 of the datasheet i linked above.

10-bit unsigned integer stallGuard2
measurement value. A higher value indicates
lower mechanical load. A lower value indicates
a higher load and therefore a higher load angle.
For stall detection, adjust SGT to return an SG
value of 0 or slightly higher upon maximum
motor load before stall.

@DocTrucker said in 4 motors and drivers for same axis:

The order of the lead screw definitions should match the order of order of probe points in the bed.g file.

Actually, the order of the probe points doesn't matter. But the order of the leadscrew coordinates in M671 must match the order of the corresponding Z motors in M584.