I've had similar problems that have made me think that there was a bug in the laser firmware (I'm using a ULS laser). However, I almost always find that there is a hidden duplicate line at that location in the drawing. One way to find these tough buggers is to open the Object Manager in Corel and just click down each entry looking for something that lights up the handles right under your problem. Delete it and see if the graphic stays or disappears. If it stays, the line was a duplicate. If it goes, redraw it and hope that fixes it.