u/Artem1nou

Cast iron I had for a while, bought it new and seasoned it, works like a charm with a little care and lubricant but what is this weird stain looking thing? Shows up after washing mostly, sometimes its just a little but sometimes its bigger liker in the picture, drying it on medium heat. What's happening, what do I do? I was thinking giving it a good scrub with fine wool and re season it.