My deepest condolences. It's always hard to lose something you've been working on for so long.

Careful cleaning of tools and maybe a good vapor lock would help next time. These locks keep out air but allow gasses to excape. Black mold may also be present in your house, like maybe in the walls. NOT good to have that kind of black mold spore floating around contaminating things. It may help, next time to cover it with a good clean cloth, as well as add a bit more salt or acid to the surface to protect the future batches. Also keeping the cabbage well submerged can prevent mold from contaminating it. Sorry!