I guess you need to re adjust your drawings, make it wider on the thin parts, as the laser fires on the thin part it will superheat to the extent it will burn itself because there`s no enough heat transfer, thin superheated material tends to be combustible that`s why it burns the material itself even if you crank up the pressure of the tip blower, it happens so quickly that there`s no cure for that aside from adjusting it, make it thick a little bit then problem solved, it cost a bit of material but at least it cuts perfectly with no burns.