Ortur 20W do not go to 0% power with S0 command

I tried to engrave papercardboard using lightburn , and I have trie at least 15 different configuartions. All of them reaches nice results BUT all of them leaves tiny imperfections in the surface that shouldn´t be touched by the laser beam.

I also have tried to subtitute M4 for M3 at the begining of the file: sames results.

¿any sugestion?

There are Travel moves, but i don not burn using lightburn, a export the file and after that reimport it in lasergrbl