Vertical Engraving drops down

[ShevonCooray]

This happened few times only when engraved in vertical direction(on y axis). Then again if I engrave again, (in same direction)it engrave perfectly fine. Anyone know the reason for this?
LaserGRBL version 5.7.0

[arkypita]

Your engraver has mechanic friction that does not allow engines to respect commanded step, or your motors does not have enough power