Engraving - output is sometimes wavy

I have been very happy with my board purchase and the laserburn software - however, i have no run into a problem with ‘wavy’ output on a complex engraving task. First trial was onto cardboard at 160mm/s and the wavy output made me think that I was traveling too fast for the line engraving I was doing and changes of direction were the cause of my problem. Reduced speed to 100mm/s and got a good engraving again on cardboard. Ran my final on plywood and it is not satisfactory. (source data for laserburn is a pdf from Coreldraw and laserburn has every element spot on the right place). Appreciate any help on resolving this,

“wavy” output? Can you post a picture of what you mean?