Missing engrave lines on china blue 3050

"few lines are engraved on the same spot at the start. I can fix it by draving a smal object like circle before the fill figure to engrave on 0% power. Then the engrave lines not overlap at the beggining."
This is certainly Mechanical backlash. This can be confirmed by engraving a circle and seeing the gap. It’s most likely something is loose. Please test the motor belt drive sprocket with an Allen Key or hex key to confirm that the screws are tight.

With the amount of observed flattening in the Leading Zero in your engraving (after the traverse), this may be the cause of the inconsistent engraving. With the laser un-powered, physically move the engrave head 1mm left right and attempt to locate the cause of the looseness.

One of the idlers could have come loose and caused the drive belt tension to be lost.

The other thing that will behave like a backlash behavior is if the rail where the engrave head travels on the Gantry is sticking. I was told to keep the gantry clean and use sewing machine oil to ensure that the machine moves freely.