In round numbers, the response time of the laser power supply is 1 ms. A 0.3 mm distance at 250 mm/s requires a 1.3 ms pulse, so whatever’s under the laser gets only a fraction of the intended energy.
That’s corrected with the Scanning Offset Adjustment over a wide variety of speeds.
Measure the actual kerf width and use that to compensate an entire layer or apply Offset Shapes to single objects.
Although it’s all shiny-new, you may safely assume the mirrors are poorly aligned and the mechanical bits will have at least one loose (or missing!) screw. Devote a few hours to getting acquainted with the innards while verifying everything looks and feels good in there.