I usually have no problem welding or subtracting portions of image. BUT, once and awhile I run head into a problem. I have clicked on curved line and base of tree, can’t seem to weld together or remove bottom portion of tree?
It only works if the lower part is a closed shape. Otherwise, LightBurn can’t decide what is inside and what is outside. Make sure the lower part is a closed shape, not a group of two lines.