echo: M421 X5.00 Y5.00 Z0.00
echo: M421 X120.00 Y5.00 Z0.00
echo: M421 X5.00 Y120.00 Z0.00
echo: M421 X120.00 Y120.00 Z0.00
This means you didnt edit (and save?) your grid correctly.
Have to look at my old M503 records about the offset but it seems ok for me.
Offset on my old machine:
: echo:Home offset (mm):
Recv: echo: M206 X-4.50 Y-5.50 Z-5.40
Try to edit the grid again and view your M503 if it works, or report your grid here nsand i could help you further.