Meaning of G1 -2.000 F2400.000
G1 -2.000 F2400.000


Is not valid G-code. As you note, -2.000 should be prefixed with an axis (X,Y,Z or E).

Marlin would ignore the -2.000 bit and simply treat the command as equivalent to

G1 F2400.000


which doesn't perform any movement, but sets the feedrate for any future moves to 2400mm/min.


  x and y shouldnt have negative


Not necessarily. Even though normally printing is done in the positive quadrant, negative values can be valid. Not only in relative movement mode, but even in absolute mode (for instance, if you set the center of your bed as (0,0) or if you use a negative z-axis offset the bring the nozzle closer to the bed).