Lines when engraving

Hello All,
I purchases the X Tool D1 Pro 20W. I am noticing fine lines randomly engraving onto my workpiece. So far, I have been adjusting the speed down to see if it helps to get rid of them. Does anyone know what causes it? I’m guessing the type of engraver is not the problem, but maybe the speed I’m engraving at.

Your laser should not be ‘on’ when it not supposed to be…

A photo results would be nice.