This is just a guess, but could it be slugs? I don't know if they like eating Dracaenas, but they to come out at night and prefer eating newer, younger leaves that are more tender than older leaves. Do you grow it indoors or outdoors? Some pics would help us to properly diagnose what could possibly be doing this.

I grow my Dracaenas outside during the warm months, but I keep them all on a table, up off of the ground and away from these annoying pests.

Have you made any progress figuring out what's eating your tree? If you can add a pic to this discussion, someone may recognize the pattern of damage.